Idlender in separate repository

Idlender as a stand-alone utility library.

Advantages of using Idlender:

• small ids (advantageous for varint encodings)
• small set of active ids
• makes segmentation of id space possible
  • multiple infinitely running threads receive id space segment. ids must be in a thread's id space segment.

Workload parameters:

• uniformly distributed "borrow" times, low variance.
• low task duration ("borrow" until "return") in comparison to task interval (between "borrow" operations)
• reset intervals during which no "borrow" operations are performed and active tasks "return" their ids