Check malloc failed

bugfix: Kernel#!=, and add #!= testcase.

Cleanup around mrb_raise calls

Add fib39.rb to benchmark/

At the first time, mrb_realloc raise RuntimeError.
At the time fails twice in a row, it causes panic.

Fix the calc_crc_16_ccitt signature to match the source file

Remove the bit-field by mrb_value.tt

Cleanup numeric.c

Add null char terminate to each symbol name.

 Export mrb_flo_to_str() as API.

 Add new API mrb_flo_to_fixnum(). You can replace mrb_flt2big() to mrb_flo_to_fixnum() with few modifications.

Fixed testrb load path

Remove API mrb_string_value(). 

Remove API mrb_string_value(). There have mrb_str_to_str() in the core. And mrb_string_value() is no merit to keep using.

Display the command line when mrbc is kicked in the verbose mode.

Simplify dump/load