Bump version to 20181019

Add MRI 2.5.3.

add MRI 2.5.2, 2.4.5 and 2.3.8

Added generate script for rbx definitions used postmodern/ruby-versions.

Add TruffleRuby 1.0.0-rc7

Add definition for TruffleRuby 1.0.0-rc6

Definitions for Rubinius 3.106 and 3.107

Fix missing space since openssl-1.1.0i update

Allow overriding HTTP client type based on environment variable of `RUBY_BUILD_HTTP_CLIENT`

More portable rename after tarball extraction

* make_package() assumes the archive was extracted to $package_name.
* fetch_tarball() does not check the name of the toplevel directory in
  the archive, so rename after if it's not exactly "$package_name".

* This reverts commit d155b41e.
* tar's --strip-components does not seem supported on OpenBSD, even
  though bsdtar does support it.
  See https://github.com/rbenv/ruby-build/commit/d155b41e#commitcomment-30215955

Upgrade to OpenSSL 1.0.2p and 1.1.0i

Add definition for TruffleRuby 1.0.0-rc5

Remove early check for LLVM when installing TruffleRuby

* TruffleRuby already checks for LLVM itself when it needs it and
  looks up more paths to find the LLVM executables clang and opt.
* See https://github.com/oracle/truffleruby/issues/1386.

Add definition for TruffleRuby 1.0.0 RC3

Add mruby 1.4.0 and mruby 1.4.1