Add break to default case in switch statement

Improve Android platform support.

Define mrb_bool_t.

Cleanup symbol.c.

Clean up parse.y.

Remove compiler warning

It is safer than applying 1bit bit-fields to signed int.

For forward compatibility, you should substiture only 1 or 0 for the variable typed mrb_bool.

Add the type check in mrb_str_to_cstr().

Extract stack zero filling into new function.

DATA_TYPE must be set as soon as possible

mrb_sys_fail raises an instance of (subclass of) SystemCallError if we have it

Cut off eval_test from main

Add null check

Extract stack zero filling to stack_clear(). Porting evelopers can optimize by replacing to memset() on their own risk.

Remove str_alloc(). Use mrb_obj_alloc_string() instead.