Use `%g` instead of `%e` for float representation in dump format

Improve compatibility to CRuby for `Float#to_s`

For conforming C standard.

Bfore:

  Float::INFINITY.to_s  #=> "inf"
  50.0.to_s             #=> "50"
  1e20.to_s             #=> "1e+20"

After / CRuby:

  Float::INFINITY.to_s  #=> "Infinity"
  50.0.to_s             #=> "50.0"
  1e20.to_s             #=> "1.0e+20"

Use `__send__` instead of `send`; ref #4207

`%g` use shorter representation than `%e`.

Remove duplicate code in numeric.c

Change the order of "expected" and "actual" in test

Fix dump/load float leteral evaluate to infinity

Add `Time` object creation API

Example:

  # example.rb
  p(2e308)
  p(-2e308)

  Good:

    $ bin/mruby example.rb
    inf
    -inf

  Bad:

    $ bin/mrbc example.rb
    $ bin/mruby -b example.mrb
    0
    -0

Cause:

  Float infinity representation is `inf` on dump and it is converted by
  corresponding `String#to_f` on load.

Treatment:

  - Introduce new representations (`i`: +infinity, `I`: -infinity)
  - Allow old representations (`inf`, `-inf`, `infinity`, `-infinity`) too
  - Raise error for unknown representations (use corresponding `Kernel#Float`)

Fix `0.0` and `-0.0` handling.

Fix the following issue:

    Good:
    $ bin/mruby -e 'p(-0.0)' #=> "-0"

    Bad:
    $ bin/mruby -e 'a=0.0; p(-0.0)' #=> "0"

Add `assert_same` and `assert_not_same`

Integrate mrblib/float.rb into src/numeric.c

- Avoid hack for `MRB_WITHOUT_FLOAT` in build scripts
- Avoid runtime dispatch for `MRB_WITHOUT_FLOAT`

Add enumerator chain feature (CRuby-2.6 compatible)

range: Refactor range.h/range.c

Add proc composition feature (CRuby-2.6 compatible)

pack: Remove redundant float check in pack_utf8()

Functions order, name, linkage and so on.

The argument is converted to fixnum before calling.

  - Enumerator::Chain
  - Enumerable#chain
  - Enumerable#+

  - Proc#<< and Proc#>>
  - Method#<< and Method#>>

io: Skip TTY test for environments that TTY device is unavailable.

range: Embed edges in RRange on boxing environment.