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
Merge remote-tracking branch 'upstream/master' into issue-653
Look for plugins under the source directory by default
Add TomDoc
Merge branch 'master' into issue-653
first pass at --drafts flag
fix tests
add drafts.feature
Improve error message for malformed highlight tags
Added the --future switch back to the CLI
Added in --limit-posts
fix whitespace in drafts.feature
Cleaner output when generating site.
Improved output for auto-regeneration.
Reworking errors with configuration file.
Updating tests for new config output.
Allow symlinked folders in unsafe mode
Now uses the more semantically correct AND operator
Remove migrator files from jekyll.gemspec

Some files no longer exists but was not removed from jekyll.gemspec:
- lib/jekyll/commands/migrate.rb 
- lib/jekyll/migrators/*.rb
Merge pull request #799 from apodlaski/remove-migrators-from-gemspec

Remove migrator files from jekyll.gemspec