A simple C hash table based on Lua's table implementation. This version does
*not* include any of Lua's special-case numeric array handling.

Example:

    table_t table;
    table_init(&table, H_STRING, NULL, NULL);
    table_set(&table, (hvalue_t)"foo", 1);
    table_set(&table, (hvalue_t)"bar", 2);
    table_get(&table, (hvalue_t)"foo");  // 1
    table_get(&table, (hvalue_t)"bar");  // 2
    table_get(&table, (hvalue_t)"baz");  // 0
    table_destroy(&table);