Add link to Drupal.org Contrib, reformat

Reformatted as proper MarkDown.
Enable Tag Entity

Change-Id: I5bac6a650e260dc3124b270b7a6c522883592cca
Code style & docs.
Code style cleanup.

Lots of code style cleanup, would like review on the following points
especially -

* Removal of CiviCRM copyright statements. Should these be included?
* Move of civicrm_entity_enable() to .install.
* Small changes to civicrm_entity_rules_event_info() for easier reading.
* Minor changes to civicrm_entity_action_load_user() to separately load
domain ID. (Cache this statically to reduce lookups?)
Label callback for contacts. I want this to use drupal_alter() but it is late and not working right now.

Conflicts:
	civicrm_entity.module
Merge remote-tracking branch 'origin/7.x-1.x' into 7.x-1.x
Merge branch '7.x-1.x-labels' into 7.x-1.x