Update README.md

Update compilation instructions and point off to documentation and
wiki pages for more details.
Update top-level headers to make them a bit more verbose
Merge pull request #257 from bitiotic/update-readme-2

Update README.md
Tree, javadocs.
Merge remote-tracking branch 'origin/master'
updated IKVM build
Merge branch 'master' of github.com:libgdx/libgdx
Merge branch 'master' into mapsapi