Extract category_link filter from category_generator.rb plugin

Allows category_link to be used as a filter to display a link to
any category.
Added robots.txt, with sitemap link
Do not strip trailing slash of canonical URLs.

Usually, links for posts are generated with a trailing slash, but
canonical URLs aren't.  Some services (e.g. http://b.hatena.ne.jp/)
are confused with that behavior.

We can fix it by removing canonical URLs, but then anyone may read
a post with /index.html URL and post the URL to some tool or service.
Therefore rel="canonical" seems useful IMHO.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Merge pull request #592 from omasanori/fix-rel-canonical

Do not strip trailing slash of canonical URLs.
Adding .powrc to allow RVM to work when POW is updated to version 0.4.0 and beyond.

Support for automatically handling .rvmrc files in projects is being deprecated in
POW version 0.4.0 and beyond. RVM will still work but project will need to have a
.powrc file that detects the presence of and then loads RVM.

The code in the .powrc could also be in the .powenv file, however the .powrc loads
first and is the configuration file recommended for inclusion in version control.
Merge pull request #602 from zan5hin/powrc

Adding .powrc to allow RVM to work when POW is updated to version 0.4.0 ...
Example repo URL - see Github issue 516
Updated Github API to V3.

Github API V2 has been removed.  The response data format also changed.
Updated Github API to V3.

Github API V2 has been removed.  The response data format also changed.
Merge pull request #666 from nathanl/example_repo_url

Example repo URL - see Github issue 516
Updated gems and rubies to 1.9.3
Merge branch 'master' of github.com:imathis/octopress
Fix for issue #622

The filters bundled with Octopress are not applied to files ending in 
`.md`, because the match in octopress_filters.rb does not match `.md`.
Merge pull request #706 from Confusion/patch-1

Fix for issue #622
bumped rbenv version fixing #743
Merge branch 'master' of github.com:imathis/octopress
Updated Github API to V3.

Github API V2 has been removed.  The response data format also changed.
Updated Github API to V3.

Github API V2 has been removed.  The response data format also changed.
Merge pull request #675 from zlu/master

Update Github API to V3
Twitter API call and links are now protocol relative