Update README.txt

* add ruby20 and ruby21 rake tasks into quick start
Merge pull request #220 from simi/patch-1

Update README.txt
Upgrade Ruby 2.0.0 to patchlevel 481

Results of 'make check':
https://gist.github.com/luislavena/628b43c0494b560aa256
Match Quick start instructions
Update year in LICENSE files

RubyInstaller has been around for 7 years already...

Time flies when you're having fun!
Trailing whistespace
Modify installer to support 2.1 semantinc version

Starting with Ruby 2.1, version numbers follow semantic version
schema:

https://www.ruby-lang.org/en/news/2013/12/21/semantic-versioning-after-2-1-0/
Build meta_chm absolute filename
Add task to build documentation package

Automate building and checksum calculatin to reduce manual steps
involved.
Upgrade Ruby 2.1 package to version 2.1.2
Use msys2(32bit) instead of old msys

Parallel make hangs due to msys bug.
http://sourceforge.net/p/mingw/bugs/1950/

msys2 is updated version of msys and the bug seems to be fixed.
http://mingw-users.1079350.n2.nabble.com/Status-of-MSYS2-td7582391.html

We pick up msys2 minimal dependencies to build ruby.
Need to set MSYSTEM=MINGW32 environment variable.

Default value of MSYSTEM is changed with msys2.
http://sourceforge.net/p/msys2/tickets/4/
Pass make options by MAKE_OPT environment variable

We can pass -jN to make for build speedup.
Replace mingw/gnuwin32 packages to msys2

Add perl for autoconf
Keep mintty in devkit