Fixed https://github.com/ruby/date/issues/83

https://github.com/ruby/date/commit/9731a3e732

Remove all shipped files and require path on JRuby until we can
add JRuby's extension to the gem.

Temporary workaround for #48

https://github.com/ruby/date/commit/94c3becef2

An almost universal convention for gems is to expose `Namespace::VERSION`
which makes it mcuh easier when debugging etc.

Many gems extracted from ruby don't do this, even though it would be even more
useful because they ship with ruby, so it's less clear which version it is.

https://github.com/ruby/date/commit/fef7ec18d8

`Date.parse` now raises an ArgumentError when a given date string is
longer than 128. You can configure the limit by giving `limit` keyword
arguments like `Date.parse(str, limit: 1000)`. If you pass `limit: nil`,
the limit is disabled.

Not only `Date.parse` but also the following methods are changed.

* Date._parse
* Date.parse
* DateTime.parse
* Date._iso8601
* Date.iso8601
* DateTime.iso8601
* Date._rfc3339
* Date.rfc3339
* DateTime.rfc3339
* Date._xmlschema
* Date.xmlschema
* DateTime.xmlschema
* Date._rfc2822
* Date.rfc2822
* DateTime.rfc2822
* Date._rfc822
* Date.rfc822
* DateTime.rfc822
* Date._jisx0301
* Date.jisx0301
* DateTime.jisx0301

https://github.com/ruby/date/commit/3959accef8

https://github.com/ruby/date/commit/e0a4cbc8f6

https://github.com/ruby/date/commit/e574cc9048

https://github.com/ruby/date/commit/47cca1b76b