Removed `borrow` and `returnToPool` functions, these had been deprecated in v2.
Fixes #84
Min pool size can now be same as max pool size, instead of defaulting to max -1.
Fixes #79
Change default priority to size - 1

README.md states that the default priority is "no priority - will go at end of line" yet the implementation was setting the default priority to 0 which puts them at the front of the line.
New resource requests without priority flag now to go back of the queue instead of front.
Fixes #74