velocityprofile: Support trap. velocity profile with velocity specification

Support a profile with a fraction of maximum velocity, instead of
a time, specification.
solvers: Update documentation and add degraded and undefined error codes to solver interface
solvers: Add missing return
solvers: Support changing internal parameters after construction of IKSolverVel_WDLS

Also removes an unnecessary pass-by-reference parameter.
solvers: Modify ChainJntToJacSolver to support calculating Jacobian in intermediate frames
solvers: Correctly return degraded error code if child solver indicates degraded solution in IKSolverVel_NR
cmake: Silence Eigen >= 3.2.0 warnings about deprecated Eigen2
Merge pull request #24 from snrkiwi/fixes

Miscellaneous fixes