Adding the host

Fixing the MySQL docs

'tasks' should not be preceded by '-' in examples

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.