Add filtering to Git post-receive hook (snippets, 5df28ff)

The Git post-receive hook can now be used to automatically filter out potentially confidential words or phrases so that in the resulting weblog post they will be replaced with the string "[filtered]".

For example, the term "[filtered]" will be replaced in the weblog post version of this commit message.

Signed-off-by: Greg Hurrell <greg@hurrell.net>