doc: clean ABI/API policy guide

doc: clean ABI/API policy guide

The original document written from the point of ABI versioning but later
additions make document confusing, convert document into a ABI/API
policy documentation and organize the document in subsections:
- ABI/API Deprecation
- Experimental APIs
- Library versioning
- ABI versioning

Aim to clarify confusion between deprecation versioned ABI and overall
ABI/API deprecation, also ABI versioning and Library versioning by
organizing the sections.

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Kevin Traynor <ktraynor@redhat.com>