Add a benchmark test for the object pool

[codemercenary]

ObjectPool will need to be a performant type. Add a benchmark so we can track its improvement. Current object pool times show ObjectPool as about 4x slower than malloc for flat datatypes, and 2x slower than malloc for types that allocate additional memory. This is clearly an unacceptable situation.

Addresses #674

[codemercenary]

Current benchmarks:

objpool
basic                                   68.542  ns  100.00%
complex                                 219.18  ns  319.77%
pool_basic                              378.65  ns  552.43%
pool_complex                            383.64  ns  559.71%