Support local variables information dumping.
Implement Kernel.local_variables for testing dumped local variables information.
Remove `lv_len` and use `nlocals - 1` instead.
Check that `lv`'s length is always `nlocals - 1`.
add Mrbtest::FIXNUM_{MAX,MIN,BIT}
test fixnum overflow for add, sub and mul
fix memcpy-param-overlap
Add Hash#invert
Refactor mrb_str_capitalize_bang()
Refactor mrb_str_downcase_bang()
Refactor mrb_str_split_m()
Refactor mrb_str_upcase_bang
Refacotr mrb_str_substr()
Refactor mrb_str_hash()
Fix indents in mrb_str_inspect() of string.c
Refactor read_lineno_record_1() in load.c
Merge pull request #2192 from suzukaze/add-hash.invert

Add Hash#invert
Merge pull request #2193 from suzukaze/refactor-string.c

Use mrb_bool instead of mrb_int  in string.c
Merge pull request #2195 from suzukaze/fix-indent-string.c

Fix indents in mrb_str_inspect() of string.c
Add Hash#keep_if
Merge pull request #2194 from suzukaze/refactor-string.c2

Refactor string.c