Check if user is in a repo before `feature list` starts.

This prevents `feature list` from listing a bunch of error messages.
Check if in a repo before all feature/hotfix commands.

Don't check if asking for --help.
Use devBranch for listing branches.

Raise exception if type is not merged or unmerged.
Raise exception in hotfix_branches as well.

And add periods to both statements.
Add list documentation.
Correct help flag logic.
Feature finish has an optional argument.

It's optional argument was not entirely documented.
Merge add-list-docs (#87) into master

Add documentation for '-v' arg for feature/hotfix list.

'-v' is an argument available for both feature and hotfix list that has
not been documented (until now!).
Merge use-developement-branch-for-feature-list (#84) into master

Use devBranch for listing branches.

Fixes #64.

Raise exception if type is not merged or unmerged.
Merge check-for-git-repo-for-feature-list (#82) into master

Check if user is in a repo before `feature list` starts.

This prevents `feature list` from listing a bunch of error messages:

```
rchoudhury@cominor ~
> feature list
fatal: Not a git repository (or any parent up to mount point /mnt/ebs)
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
fatal: Not a git repository (or any parent up to mount point /mnt/ebs)
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).

Current Branch:
------------------------------------------------------------
fatal: Not a git repository (or any parent up to mount point /mnt/ebs)
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
(not on any branch!)

Available feature branches:
------------------------------------------------------------
(none)
fatal: Not a git repository (or any parent up to mount point /mnt/ebs)
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
/mnt/ebs/home/ifixit/git-scripts/lib/helpers.rb:174:in `initialize': Permission denied - /git-scripts.log (Errno::EACCES)
        from /mnt/ebs/home/ifixit/git-scripts/lib/helpers.rb:174:in `open'
        from /mnt/ebs/home/ifixit/git-scripts/lib/helpers.rb:174:in `log_command'
        from /mnt/ebs/bin/feature:260:in `<main>'
```
Merge feature-finish-has-optional-arg (#88) into master

Feature finish has an optional argument.

It's optional argument was not entirely documented.
Add contributing and remove hacking portion of README.
Allow 'feature switch' to switch by pull number using -n
Switch-by-number: Abstract logic and add to hotfix
Switch-by-number: update documentation
Switch-by-number: update man docs
Add 'iFixit' back into Ronn-generated files

Had to run 'ronn filename --organization=iFixit' to add it back
Improve flow of hotfix branch-switching logic
Merge pull request #92 from iFixit/switch-by-number

Allow 'feature switch' to switch by pull number
Merge add-contributing (#91) into master

Add CONTRIBUTING.md.

Remove the hacking section from the README and place it in CONTRIBUTING.
This takes advantage of github's nifty little feature that allows you to
view contributing rules when filing a new issue .