Allow specifying args directly to actions using module: syntax

Makes things like
- name: do complex things with complex module
  complex:
    setting_a: true
    setting_b:
    - foo
    - bar
possible.

Fixes #2228.
Allow (local_)action: to be a dict

Use the key module: to set which module to invoke.
Ensure complex_args is considered in all action_plugins
add to_nice_yaml|json filters
Add mysql user documentation
Merge pull request #2234 from akvadrako/nice-yaml-and-json

add to_nice_yaml|json filters
Merge pull request #2235 from marktheunissen/mysql-idempotent-explanation

Add mysql user documentation about idempotent playbooks
Merge pull request #2232 from dhozac/module-args-dict

Allow specifying args directly to actions using module: syntax
Update documentation on complex args to new simpler format.