Tighter inspect

Sets up inspect for `Sawyer::Resource` and `Sawyer::Resource#rels` to look like hashes.

`Sawyer::Resource` before:
```
[2] pry(main)> r = o.repo 'lostisland/sawyer'
=> #<Sawyer::Resource:0x007f8c527e89f8
 @_agent=<Sawyer::Agent https://api.github.com/>,
 @_fields=
  #<Set: {:id,
   :name,
   :full_name,
   :owner,
   :private,
   :description,
   :fork,
   :created_at,
   :updated_at,
   :pushed_at,
   :homepage,
   :size,
   :stargazers_count,
   :watchers_count,
   :language,
   :has_issues,
   :has_downloads,
   :has_wiki,
   :forks_count,
   :open_issues_count,
   :forks,
   :open_issues,
   :watchers,
   :default_branch,
   :master_branch,
   :permissions,
   :organization,
   :network_count,
   :subscribers_count}>,
 @_metaclass=#<Class:#<Sawyer::Resource:0x007f8c527e89f8>>,
 @_rels=
  #<Sawyer::Relation::Map: [:html, :self, :forks, :keys, :collaborators, :teams, :hooks, :issue_events, :events, :assignees, :bra
 @attrs=
  {:id=>2544008,
   :name=>"sawyer",
   :full_name=>"lostisland/sawyer",
   :owner=>
    #<Sawyer::Resource:0x007f8c5581ca70
     @_agent=<Sawyer::Agent https://api.github.com/>,
     @_fields=#<Set: {:login, :id, :gravatar_id, :type, :site_admin}>,
     @_metaclass=#<Class:#<Sawyer::Resource:0x007f8c5581ca70>>,
     @_rels=
      #<Sawyer::Relation::Map: [:avatar, :self, :html, :followers, :following, :gists, :starred, :subscriptions, :organizations, 
     @attrs=
      {:login=>"lostisland",
       :id=>2613464,
       :gravatar_id=>"2cac6a53fb519390129fb847ca365f31",
       :type=>"Organization",
       :site_admin=>false}>,
   :private=>false,
   :description=>"Secret User Agent of HTTP",
   :fork=>false,
   :created_at=>2011-10-09 19:15:53 UTC,
   :updated_at=>2014-01-21 16:06:43 UTC,
   :pushed_at=>2014-01-21 16:06:42 UTC,
   :homepage=>"",
   :size=>588,
   :stargazers_count=>89,
   :watchers_count=>89,
   :language=>"Ruby",
   :has_issues=>true,
   :has_downloads=>true,
   :has_wiki=>true,
   :forks_count=>19,
   :open_issues_count=>4,
   :forks=>19,
   :open_issues=>4,
   :watchers=>89,
   :default_branch=>"master",
   :master_branch=>"master",
   :permissions=>
    #<Sawyer::Resource:0x007f8c5583ba60
     @_agent=<Sawyer::Agent https://api.github.com/>,
     @_fields=#<Set: {:admin, :push, :pull}>,
     @_metaclass=#<Class:#<Sawyer::Resource:0x007f8c5583ba60>>,
     @_rels=#<Sawyer::Relation::Map: []>,
     @attrs={:admin=>false, :push=>false, :pull=>true}>,
   :organization=>
    #<Sawyer::Resource:0x007f8c5583a930
     @_agent=<Sawyer::Agent https://api.github.com/>,
     @_fields=#<Set: {:login, :id, :gravatar_id, :type, :site_admin}>,
     @_metaclass=#<Class:#<Sawyer::Resource:0x007f8c5583a930>>,
     @_rels=
      #<Sawyer::Relation::Map: [:avatar, :self, :html, :followers, :following, :gists, :starred, :subscriptions, :organizations, 
     @attrs=
      {:login=>"lostisland",
       :id=>2613464,
       :gravatar_id=>"2cac6a53fb519390129fb847ca365f31",
       :type=>"Organization",
       :site_admin=>false}>,
   :network_count=>19,
   :subscribers_count=>8}>
```

`Sawyer::Resource` after:
```
[1] pry(main)> r = o.repo 'lostisland/sawyer'
=> {:id=>2544008,
 :name=>"sawyer",
 :full_name=>"lostisland/sawyer",
 :owner=>
  {:login=>"lostisland",
   :id=>2613464,
   :gravatar_id=>"2cac6a53fb519390129fb847ca365f31",
   :type=>"Organization",
   :site_admin=>false},
 :private=>false,
 :description=>"Secret User Agent of HTTP",
 :fork=>false,
 :created_at=>2011-10-09 19:15:53 UTC,
 :updated_at=>2014-01-21 16:06:43 UTC,
 :pushed_at=>2014-01-21 16:06:42 UTC,
 :homepage=>"",
 :size=>588,
 :stargazers_count=>89,
 :watchers_count=>89,
 :language=>"Ruby",
 :has_issues=>true,
 :has_downloads=>true,
 :has_wiki=>true,
 :forks_count=>19,
 :open_issues_count=>4,
 :forks=>19,
 :open_issues=>4,
 :watchers=>89,
 :default_branch=>"master",
 :master_branch=>"master",
 :permissions=>{:admin=>false, :push=>false, :pull=>true},
 :organization=>
  {:login=>"lostisland",
   :id=>2613464,
   :gravatar_id=>"2cac6a53fb519390129fb847ca365f31",
   :type=>"Organization",
   :site_admin=>false},
 :network_count=>19,
 :subscribers_count=>8}
```

`Sawyer::Relation::Map` before:
```
[3] pry(main)> r.rels
=> #<Sawyer::Relation::Map: [:html, :self, :forks, :keys, :collaborators, :teams, :hooks, :issue_events, :events, :assignees, :branches, :tags, :blobs, :git_tags, :git_refs, :trees, :statuses, :languages, :stargazers, :contributors, :subscribers, :subscription, :commits, :git_commits, :comments, :issue_comment, :contents, :compare, :merges, :archive, :downloads, :issues, :pulls, :milestones, :notifications, :labels, :releases, :git, :ssh, :clone, :svn]>
```

`Sawyer::Relation::Map` after:
```
[2] pry(main)> r.rels
=> {:html_url=>"https://github.com/lostisland/sawyer",
 :self_url=>"https://api.github.com/repos/lostisland/sawyer",
 :forks_url=>"https://api.github.com/repos/lostisland/sawyer/forks",
 :keys_url=>"https://api.github.com/repos/lostisland/sawyer/keys",
 :collaborators_url=>
  "https://api.github.com/repos/lostisland/sawyer/collaborators",
 :teams_url=>"https://api.github.com/repos/lostisland/sawyer/teams",
 :hooks_url=>"https://api.github.com/repos/lostisland/sawyer/hooks",
 :issue_events_url=>
  "https://api.github.com/repos/lostisland/sawyer/issues/events",
 :events_url=>"https://api.github.com/repos/lostisland/sawyer/events",
 :assignees_url=>"https://api.github.com/repos/lostisland/sawyer/assignees",
 :branches_url=>"https://api.github.com/repos/lostisland/sawyer/branches",
 :tags_url=>"https://api.github.com/repos/lostisland/sawyer/tags",
 :blobs_url=>"https://api.github.com/repos/lostisland/sawyer/git/blobs",
 :git_tags_url=>"https://api.github.com/repos/lostisland/sawyer/git/tags",
 :git_refs_url=>"https://api.github.com/repos/lostisland/sawyer/git/refs",
 :trees_url=>"https://api.github.com/repos/lostisland/sawyer/git/trees",
 :statuses_url=>"https://api.github.com/repos/lostisland/sawyer/statuses/",
 :languages_url=>"https://api.github.com/repos/lostisland/sawyer/languages",
 :stargazers_url=>"https://api.github.com/repos/lostisland/sawyer/stargazers",
 :contributors_url=>
  "https://api.github.com/repos/lostisland/sawyer/contributors",
 :subscribers_url=>
  "https://api.github.com/repos/lostisland/sawyer/subscribers",
 :subscription_url=>
  "https://api.github.com/repos/lostisland/sawyer/subscription",
 :commits_url=>"https://api.github.com/repos/lostisland/sawyer/commits",
 :git_commits_url=>
  "https://api.github.com/repos/lostisland/sawyer/git/commits",
 :comments_url=>"https://api.github.com/repos/lostisland/sawyer/comments",
 :issue_comment_url=>
  "https://api.github.com/repos/lostisland/sawyer/issues/comments/",
 :contents_url=>"https://api.github.com/repos/lostisland/sawyer/contents/",
 :compare_url=>"https://api.github.com/repos/lostisland/sawyer/compare/...",
 :merges_url=>"https://api.github.com/repos/lostisland/sawyer/merges",
 :archive_url=>"https://api.github.com/repos/lostisland/sawyer/",
 :downloads_url=>"https://api.github.com/repos/lostisland/sawyer/downloads",
 :issues_url=>"https://api.github.com/repos/lostisland/sawyer/issues",
 :pulls_url=>"https://api.github.com/repos/lostisland/sawyer/pulls",
 :milestones_url=>"https://api.github.com/repos/lostisland/sawyer/milestones",
 :notifications_url=>
  "https://api.github.com/repos/lostisland/sawyer/notifications",
 :labels_url=>"https://api.github.com/repos/lostisland/sawyer/labels",
 :releases_url=>"https://api.github.com/repos/lostisland/sawyer/releases",
 :git_url=>"git://github.com/lostisland/sawyer.git",
 :ssh_url=>"git@github.com:lostisland/sawyer.git",
 :clone_url=>"https://github.com/lostisland/sawyer.git",
 :svn_url=>"https://github.com/lostisland/sawyer"}
```