mrb_str_pool add string capa

src/string.c RESIZE_CAPA use safe name variables

* add multi value support
* `each` method may not rewind the sequence so that `cycle` should save elements

Add Enumerable#cycle

This has a possibility of naming conflicts

Add Enumerable#reverse_each

Implement \u notation for strings and regexes.

This change adds the \u notation for double quoted strings and regular
expressions.  It does not implement the \u notation for character literals.
Both the \uNNNN and \u{NNNN} notations are supported.

\uNNNN is implemented by emitting equivalent UTF-8; that is, "\u4000" is
equivalent to "\xE4\x80\x80".

Unlike CRuby, the \u{NNNN} notation allows only one character per pair of
braces; I see no way to lift this restriction without remodeling the parser.

Hash#__update fix typo

Count crashed tests in total tests count.

It's called by create Hash of over 126 keys

Add Enumerable#one?

Hash#{reject,reject!} support return Enumerator

Use MRB_ARGS_REST() instead of ARGS_REST()

Hash#{select,select!} support return Enumerator

Add Enumerable.none?

if non block given