Make OP_ASGN faster.

chipKitMax32 target example

Adjust stack position of NODE_RESCUE.

I think that `*=` and `/=` can be compiled to `OP_MUL` and `OP_DIV`.

Reduce sprintf() calls. Remove mrb_int_to_str() and MRB_INT_FORMAT.

Fix errors caused by stdio.h dependent code.

Remove commented out code. Remove redundant function calls.

Support to build on pwd != mruby source root

Fix mrb_fix2str().

Clean numeric.c up.

Fix an underlying bug. flodivmod() will be crashed in case ((y == 0) && ((divp == NULL) || (modp == NULL))).

Fix mrb_fix2str() to enable handling some negative values correctly. This fix is based on @cremno's hack. It will fix #869.

Regexp compile

Clean up mrbconf.h

fix access denied error at incremental build

- undef for windows is not used by default so comment it
- casting to the same type is not needed
- parenthesis are not needed for macro attributes separated by commas
- change order of MRB_NAN_BOXING and MRB_INT64 to simplify logic