convert exception message to string

Move src/re.h to include/mruby/re.h . 

fixes: mruby -e "p ArgumentError.new(1)"

Refactor numeric.c

Add test for UTF-8 string String#size .

OP_EQ系が速くなった

Improve Language Documentation

exc_inspect: dup file and check mesg only once

reduce RSTRING_PTR usage

mruby-time: two small changes for portability

>If the calendar time cannot be represented, the function returns the
value (time_t)(-1).
http://www.iso-9899.info/n1256.html#7.23.2.3p3

The gem doesn't use the global variables and:
>Local timezone information is used as though localtime() calls tzset().
http://pubs.opengroup.org/onlinepubs/9699919799/functions/localtime.html