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
Improve error message for malformed highlight tags
Allow symlinked folders in unsafe mode
Now uses the more semantically correct AND operator
Merge branch 'master' into issue-653
Add back a test that was mistakenly removed.
Rename setup_plugins to plugins_path
Fix up the whitespace.

Remove an extra blank line and fix another whitespace error pointed out
by git diff
Merge pull request #654 from mattr-/issue-653

Look for plugins under the source directory. Fixes #653.
Update history to reflect merge of #654
Add tests for filtering symlink entries when safe mode enabled
Merge pull request #824 from sinamt/symlinked_folders

Allow symlinked folders in unsafe mode (with tests). Closes #796, resolves #233.
Update history to reflect merge of #824.
Merge pull request #785 from lenniboy/master

Improve debugability of error message for a malformed highlight tag
Update history to reflect merge of #785.