Add Chris Kennelly to the contributors list.
Include stddef.h for size_t.
Setup targets from each directory, rather than the top-level.
Partially resolve google/benchmark#17 by fixing regular expression leak.

This adds a unit test to validate the wrapper without running the entirety of
benchmark_test.
Resolve memory leak from benchmark instances in google/benchmark#17.

This shifts registration from a global vector to a singleton that manages
benchmark destruction during shutdown.