fix various documentation xrefs

Fix documentation example for the fail module

The example for the fail module doesn't work:
  http://www.ansibleworks.com/docs/modules.html#fail

The current text shows:
    - fail: msg="The system may not be provisioned according to the CMDB status."
      when: "{{ cmdb_status }} != 'to-be-staged'"

The "when" documentation indicates that the argument is already a Jinja2
expression:
  http://www.ansibleworks.com/docs/playbooks_conditionals.html#the-when-statement

Thus, the following is
      when: cmdb_status != "to-be-staged"

is preferred even though the following could work but generates a
deprecation warning:
      when: {{cmdb_status != "to-be-staged"}}

added more usefull example for jinja2 overrides 

Missing "is" in file module description

Updated main description to state that the yum module will handle package groups.  Added descriptions for each example, as it is unclear to (some) users that @Name implies a group install.

used)

Signed-off-by: Brian Coca <briancoca+dev@gmail.com>

Add note about how to submit doc changes to generated module docs, limit TOC depth for module category list.

out of github.

Fixed syntax error and removed unused imports

shell module: document removes option and sync with command module doc