Apply suggested fixes by Simo after code review
* return statements no longer use () unless it's an expression
* remove all use of assert() in library
* use bool,true,false instead of int,TRUE,FALSE
* add check for NULL hash table in public entry points
* example code in header file now a seperate file

* assure consistent use of unsigned long data type
* add more debugging support
* break out generation of integer key into convert_key() function

* table parameters now tunable rather than hardcoded
* table can now accept custom alloc()/free() functions
* add function create_table_ex() to pass extra table parameters
* remove MUL(), DIV(), MOD() macros
* hash statistics now separate struct which can be queried
* test program now accepts tuning parameters, iteration count; has better error checking and reporting

fix min/max load factor comman line args in test program