Added possibility to compile without murmur

This patch adds the possibility to compile without murmur included, for
adding own hash functions on runtime.

It includes:
- outsourcing of HashFunc type definition
- macros for compiling with or without murmur
- HashFunc entries in main hashtable structure
added missing asterisks
added compile task for compiling without murmur
added hash function pointer passing if compiled without murmur
Merge pull request #8 from matthiasbeyer/murmur_optional_alternative

Murmur optional alternative