member: implement main API

member: implement main API

Membership library is an extension and generalization of a traditional
filter (for example Bloom Filter and cuckoo filter) structure.
In general, the Membership library is a data structure that provides a
"set-summary" and responds to set-membership queries of whether a
certain element belongs to a set(s). A membership test for an element
will return the set this element belongs to or not-found if the
element is never inserted into the set-summary.

The results of the membership test are not 100% accurate. Certain
false positive or false negative probability could exist. However,
comparing to a "full-blown" complete list of elements, a "set-summary"
is memory efficient and fast on lookup.

This patch adds the main API definition.

Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
Reviewed-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>