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
Merge pull request #2210 from yui-knk/fix-typo

fix typo
Add tests for Range#to_s Range#inspect.
Add Hash#key
OP_ENTER clean block object in register
Add ISO No. to String#inspect test.
Merge pull request #2212 from yui-knk/add-range-test

Add tests for Range#to_s Range#inspect.
Merge pull request #2213 from suzukaze/add-hash.key

Add Hash#key
Merge pull request #2215 from yui-knk/fix-typo-test

Add ISO No. to String#inspect test.
Merge pull request #2214 from ksss/proc-clear

OP_ENTER clean block object in register
libreadline requires libtermcap on OpenBSD.
Merge pull request #2216 from iij/pr-mirb-link-termcap

libreadline requires libtermcap on OpenBSD.
Move `__method__` to mruby-kernel-ext since it's not ISO method.
pacify MSVC warnings for time.c
Refactoring test to use assert_nothing_raised.
Remove use of mruby-proc-ext method.