Fix style and add copyright to testForwardKinematics.cpp
Fix style and add some comment for Skeleton
Include nlopt to core dependencies
evalGradient() and evalHessian() are not pure virtual functions
Minor change:
- Lower xtol for nlopt solver
Add basic inverse kinematics solver using optimization
Include nlopt to core dependencies (fix CMakeLists.txt)
Add initial guess for solving inverse kinematics
Rename: ObjFuncTramsfDis --> InvKinObjFunc
Fix testInverseKinematics by changing nlopt solver option
Update Changelog.md and Migration.md
Move and rename from Skeleton::solveInvKinematics() to BodyNode::fitTransform()

Add BodyNode::fitLinearVel() and BodyNode::fitAngularVel()
Update Changelog.md
Fix compile error in debug mode
Fix BodyNode::fitWorldLinearVel() and BodyNode::fitWorldAngularVel()

When the linear velocity is being fitted, angular velocity is fixed and vice versa.
Better naming for functions and variables of optimizer
Merge pull request #154 from dartsim/inverse_kinematics

Add basic inverse kinematics functions