ref #3492 #3515 #3517

This reverts commit d2cad9ac.

To avoid redundant `mark_context()`.

Fix space flag with inf/nan

Fix embedded document with unterminated terminator

`skips()` is `mrb_bool` function, should return `FALSE` at EOF, not
`EOF`.

As for non-finite float, calculate the exact needed size with the
space flag.

While `"% 2f"` and `"% 4f"` result in `" Inf"` and `" Inf"`
respectively, `"% 3f"` results in `"Inf"` (no space).

Add --libmruby-path support to mruby-bin-mruby-config.

Reopens #3612.

Reopens #3550. Those 2 issues are exclusive.

Support `freeze` method in `Struct`.

Fix typo in usage message.

Align pool allocator with 8 byte in 64-bit environment.

Add missing `arg_i++` to fix bug of `s!` in mrb_get_args.

To avoid warnings from undefined sanitizer.
( https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html )

A new function `mrb_yield_cont()` is provided. You have to call it
at the end of a C defined method, e.g. `return mrb_yield_cont()`.

Some examples in #3359 still behave differently from CRuby.

Omitted `goto L_RAISE` to raise an exception.

Check if sc->mt is initialized before copying it.