Experimental LockNeedles
Recovered Claim mechanism for new implementation
Renamed INeedle<T>.Release to INeedle<T>.Free
Sorted out methods

Claim vs Free
Capture vs Uncapture
Lock vs Unlock
Rollback Uncaptures the internal LockNeedle
Renamed token to needle
Fixed unnecessary calls to extension CopyTo
Added new class FlagArray

FlagArray is a thread-safe subset of BitArray.
New flagas property returns the set bits
Optimization for iteration over FlagArray
Fixed unsetting bits
Flag array will now use the array pool
Removed ArrayPool from the readme

There is a good reason for the ArrayPool being internal: it works with
array sizes that are powers of two, but there is no control on arrays
donated that are not of the proper sizes. Until this is amended
ArrayPool must remain internal.
New implementation for LockNeedles

This new implementation allows to suggest the thread capacity of the
LockNeedleContext, this ability is required to backport the Concurrent
classes.
Removed Claim

We are going to trust _freeSlots to keep track of free slots, instead of
keeping track of the thread that has requested each slot. This allows
the slots to be freed by a different thread from the one that requested
them.
Small interface improvements
[Fix] Removed wrong optimization
Renamed internal fields

_data -> _entries
Improved Contains
New Contains improvements (and fix)