This reverts commit 6dabb336.

Add mrb_utf8_from_locale, mrb_utf8_free, mrb_locale_from_utf8, mrb_locale_free. Just works for windows.

 * `mrb_show_version()`
 * `mrb_show_copyright()`

mrb_parser_new() and mrb_generate_code() may return NULL.

`PATH_MAX` doesn't have to be defined and if it is, then its value is
usually incorrect (possible buffer overflow).
Use `malloc` and `snprintf` instead to prevent this.

https://www.gnu.org/software/hurd/community/gsoc/project_ideas/maxpath.html

Fix compilation fail caused by GNU Readline and `ISPRINT`.
Also add missing `unsigned char` cast.

also allow spaces around quit/exit.

It doesn't matter to me if one is using FALSE/TRUE instead of 1/0
but I prefer a type (alias) which emphasizes boolean vars to int.
I changed 1/0 to FALSE/TRUE anyway.

remove unused and unneeded:
- sysexit_status
- type (a global variable)

add mrb_ prefix to:
- codedump_all
- class_instance_method_list
- parser_dump

make various functions static, incl.:
- yyparse
- make_exception

- reduce compile time by a little bit (full-core: ~0.7s for me)
- thanks to 'include-what-you-use' for some help
- include Standard C header files before any other (coding style)