Look for plugins under the source directory

When generating the site, Jekyll will now look for plugins under the
source directory by default. The plugin location can still be changed in
_config.yml
Bump kramdown, rake, shoulda, cucumber, redcarpet
Add test/unit
Merge remote-tracking branch 'upstream/master' into issue-653
Look for plugins under the source directory by default
Add TomDoc
Dont test kramdown

It should have it's own tests for that
Merge branch 'master' into issue-653
Ensures that categories are Strings before escaping. Fixes #759.
Added test for all-String categories.
Update command classes moving into a module
Strip extra newlines
Update converter classes moving into a module
Update pagination classes moving into a module
Update tag classes moving into a module
Remove new lines between module and class
first pass at --drafts flag
fix tests
add drafts.feature
Look for _posts directory relative to cwd, not relative to tumblr.rb.

That's where we put it earlier, so that's where we'll find it now.

This addresses part of issue #773 (subissue 3).