Added outputs to Muscle. Hooked into Thelen2003Muscle and added Thelen2003Muscle to testComponents. TODO: repeat for Millard2012EquilibriumMuscle.
Merge branch 'master' of https://github.com/opensim-org/opensim-core into addOutputsToMuscles
Outputs should now be available for Millard2012EquilibriumMuscle as well. Note that Millard2012AccelerationMuscle makes testComponents kerplode ("testComponents.exe has stopped working" error on Windows). Probably not worth investigating at this time, since nobody uses the Acceleration model.
Ignoring issues with the Acceleration muscle.
Converted output names from `CamelCase` to `lowercase_with_underscores`.
Update Millard2012EquilibriumMuscle.h
Merge branch 'master' of https://github.com/opensim-org/opensim-core into addOutputsToMuscles

Conflicts:
	OpenSim/Actuators/Millard2012EquilibriumMuscle.h
Replaced lingering `OVERRIDE_11`s with `override`.
Merge pull request #89 from opensim-org/addOutputsToMuscles

Add outputs to Thelen2003Muscle and Millard2012EquilibriumMuscle