Updating various doc items with 0.6 features, releasing soon, and removing references to things new in 0.4, which
has been out long enough to no longer be new.

Update rst/modules.rst

Minor doc fixups for apt module.

Change hyphens to underscores in argument names, e.g.:
 update-cache -> update_cache

Remove question mark in description of behavior of update_cache.

EC2 external inventory documentation

Document postgresql_db and postgresql_user modules.

Document that apt-cache=yes is equivalent to apt-get update.

Update index.html

Remove branch arg from git docs.

I propose this quote from the mailinglist should go in the "What People Are Saying" section.

Document sudo_user in playbook