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
Titles in code plugins can have slashes in them. Closes #892
Removed unnecessary regex in code block plugin
Merge pull request #408 from dtchepak/category_link_filter

Extract category_link filter from category_generator.rb plugin
updated gems
Merge pull request #537 from joseprio/master

robots.txt generation
Rake task new_post now accepts titles through stdin
This should help resolve issues for zsh users and make it easier to enter titles which freak out Rake's argument processing
removed accidentally added file
Escape github repo descriptions, as they may contain HTML.
Merge pull request #914 from rixth/master

Escape github repo descriptions, as they may contain HTML.
added last post for 2012
added first post for 2013
updated stylesheets
updated blog pages
Merge branch 'master' of git://github.com/imathis/octopress