We have a new heap implementation replacing mem_pool. Add docs on its
API and internals, and add a deprecation note to the mem_pool section.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
Move guides and APIs into separate directories and cleanup naming
introducing index files rather than named section files.
Signed-off-by: Anas Nashif <anas.nashif@intel.com>