Updated doc for semantic highlighting

Also updated the gen_manual script and re-built the manual
Merge pull request #1 from edani/faces

Updated doc for semantic highlighting
Change the documentation from compile-on-save to perform-on-save.

Corresponds to the same branch name in ensime-emacs.
Merge pull request #2 from sellout/perform-on-save

Change the documentation from compile-on-save to perform-on-save.