zunitc: Clarify documentation on return behavior.

* Clarify documentation on ZUC_ASSERT_* behavior in regards to return
   vs. abort()
* Added overview section on return behavior.
* Fixed spelling
* Removed outdated reference to tap function.

Changes since v1:

* Incorporated grammatical feedback.

Signed-off-by: Jon A. Cruz <jonc@osg.samsung.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
2 files changed