This patch slightly reduce memory consumption (2% for my test).

The issue is reported by `https://hackerone.com/dgaletic`.

Wrong pool data length for negative floating value in a mrb file.

It should be done by planned embedded symbols.

Reduce instruction size

Since our new VM instruction is byte based, there's no need to endian
conversion of instruction sequences.

By dffa203d that reclaim `env` objects from heaps, there's more chance
for `env` objects referenced from fibers may be freed from heap pages.

Fixed a bug in INIT_DISPATCH for non direct threading; fix #4153

Add debug flag to `MRuby::Build`

Keep `tr_pattern` static if possible

Rename `MRuby::Build#libmruby` stuff to avoid confusion

Add missing dependency of source code generator

Suppress sleep test script warning

Sort test script list too