Update README.md

Modified README.md to describe the purpose of the Simbody3.3 branch, which is to make only changes needed for integration with Gazebo.
Removed "(development)" note in version number for Doxygen.
Merge branch 'master' of https://github.com/j-rivero/simbody
Merge branch 'master' of https://github.com/j-rivero/simbody into simbody-3.3
Merge branch 'master' of https://github.com/simbody/simbody
Modified MobilizedBody::lock() and lockAt() methods to immediately modify q and/or u in the state to satisfy the requested lock, rather than waiting until the next prescribe() call.

This satisfies Kevin He's request in Simbody issue #20.
Add travis-ci setup file.
Get travis-ci working.
Choose compilers for travis-ci.
Add library dependencies to travis.
Add library dependencies to travis.
Add library dependencies to travis.
Add library dependencies to travis.
Add library dependencies to travis.
Reduce travis dependencies for travis.
Reduce travis dependencies for travis.
Reduce travis dependencies for travis.
Don't build examples for travis testing.
Is apt-get update necessary?
Yes, apt-get update is necessary, for now.