Add missing try-catch around main code.

Signed-off-by: Michael Sherman <msherman@stanford.edu>
Fix bug in SimbodyMatterSubsystem::multiplyByMInv() reported by Chris Dembia as issue #29 on GitHub: it was unnecessarily requiring the state to have been realized through Dynamics stage; it actually only depends on Position-level quantities. This made the method unsuited for use during a force calculation, where only position and velocity information is available.
Merge pull request #31 from sherm1/master

Fix multiplyByMInv() so it is usable in forces & controllers
Update README.md
Update README.md
Ask Travis to build with clang as well as gcc.
Merge branch 'master' of https://github.com/simbody/simbody
Fix clang warnings.
Revert "Fix clang warnings."

This reverts commit a851cc739b5d277cbda9a199e37ed5e2ab48ed65.
Fix clang warnings.
Add files for semi-implicit Euler; copied from semi-explicit Euler and changed names but no new code yet.
Merge branch 'semiImplicitEuler' of https://github.com/sherm1/simbody into semiImplicitEuler