wrapper functions for string operations to prevent side effects eg double evaluation

track deleted items, affects rehashing, fixed probing efficiency

fix typo in sse2

added README

includes memarena explicitly

doesn't include memarena by default

Added fclean targets to benchmarking

make benchmark compares scalar and NEON

SIMD for match_byte

Early return in rehash

Streamlined logic in allocate_table()

Cleaned up header file

removed prototypes that were out of implementation

added tests for strings

added support for string as keys, const to a few functions