README update

-Removed spaces between links
-Removed some now-useless stuff, and added a generalization (the
IMPORTANT part)
-Updated Java version
-Clarified Github for Windows/Mac part
-Updated for pahimar's build.xml change (ant build)
-Updated for Repository Next
(https://github.com/blog/1529-repository-next)
That should be it ;)
And updated the PR part

Sigh.
Merge pull request #394 from 50Wliu/README

Updated README.md