`gcc -O3` raises error on truncation using `snprintf`.

This time we used `Integral` module which is mruby specific.

Fix misspelling words in comments, docs

`"a".sub!("a", "a")` should not return `nil`.

`Hash#compact!` should return `nil` if the receiver does not change.

`mrb_iv_p` -> `mrb_iv_name_sym_p`
`mrb_iv_check` -> `mrb_iv_name_sym_check`

Use segment list for instance variable again to reduce memory.

The macro `RCLASS_SUPER`, `RCLASS_IV_TBL` and `RCLASS_M_TBL` are
removed from `include/mruby/class.h`.

Fix to sizeof(mrb_value) is 4 bytes with MRB_WORD_BOXING on 32-bit mode

Unless `MRB_DISABLE_STDIO` is set. `snprintf` is used anyway
if mruby is configured to use `stdio`. This change reduces 8KB
of program size on the Linux box.

This means reducing one word per a call frame.

Renamed flag macro names as well:
`MRB_FLAG_IS_FROZEN` -> `MRB_FL_OBJ_FROZEN`
`MRB_FLAG_IS_PREPENDED` -> `MRB_FL_CLASS_IS_PREPENDED`
`MRB_FLAG_IS_ORIGIN` -> `MRB_FL_CLASS_IS_ORIGIN`
`MRB_FLAG_IS_INHERITED` -> `MRB_FL_CLASS_IS_INHERITED`

[mruby-socket] Network services might not be available

add mrbc option `--remove-lv`

* refactor: move `irep_remove_lv` from `mruby-bin-strip` gem to src/dump and rename to `mrb_irep_remove_lv`
* add: mrbc option `--remove-lv` to remove LVAR section

[mruby-test] Fix task name is not necessarily a valid path

Errno::ENOENT: No such file or directory @ dir_s_mkdir - mruby:Z:/Documents

Added ~/Android/Sdk/ndk-bundle as default NDK home

Support MRB_WITHOUT_FLOAT to mruby-io

Add information about Kernel#binding

Run tests parallelly for each target.