Add more information to README.md

Add a link to the wiki page and some precompiled build information to
the README.md file.
Generalize JDK download link in README.md

The JDK download link, which is located in the README.md file, now
points to an overview page instead of a download page for a specific JDK
version.
Use apache commons lang MutableXX objects instead of AtomicXX

Replace usages of AtomicXX objects for final field modifiation with the
MutableXX classes from apache commons lang.