Fixed C declaration in re.h

mruby special.

Fixnum is usually big enough for shift width.

Reimplements Range#first

Fixed NaN boxing for 64-bit configrations

Fix typo in test

Useful for testing when using boxing on different platforms.

So that other files can immediately use it.

Definition of boxed pointer is following:
`111111111111TTTT TTPPPPPPPPPPPPPP PPPPPPPPPPPPPPPP PPPPPPPPPPPPPPPP`

Previously, only the last 32-bit were set, and remaining 14 bits were zeroed when setting `ttt`.

Range#first shouldn't call `Range#to_a` on infinity range.

Fix for sprintf test exceeding bounds with MRB_INT16

Fix Range#size results

Fix condition of Range#include?

Doc

bundled testing gems do not need to be included in default.gembox.
all gems under mrbgems are linked automatically in the test process.

Inline structures have no instance variables, no finalizer, and offer as much space as possible in RBASIC object. This means 24 bytes on 64-bit platforms and 12 bytes on 32-bit platforms.
mruby-inline-struct gem is only provided for testing.

Remove webhook notification for Travis CI

Ranges should not rewrite

As travis-rubies now uses 3 Mac jobs to create archives for various OS
releases.

This is a bit wasteful if multiple builds pass in a short period.

Instead, Travis CI is now running a nightly build of mruby-head
(around 22:30 UTC). This will happen regardless of the state of the
master branch.