More robustly validate signature inputs, closes #313
New hash_append robust container hash function framework:
* is_contiguous_hashable trait identifies optimizable types
* hash_append() function overloads for basic types:
  - scalars, floats
  - array, C array
  - pair, tuple
  - boost array and tuple (if configured)
* Provided Spooky hash wrapper for use with hash_append
* Use hash_append in hardened_hash and other places
* New Utility meta functions for working with variadics:
  - static_and
  - static_sum
* Added type_name utility function for diagnostics
* hash_metrics suite of functions to evalulate hash functions
* Test suites to measure hash function performance
* Various fixes