Allow to have multiple unconnected bodynodes in a skeleton
Merge pull request #196 from dartsim/unconnected_bodies

Merged since this change
1) does not affect on the dynamics algorithms, and
2) is required to pass gazebo unit tests
Add parsing bullet collision detector in SkelParser
Add parsing bullet collision detector in SkelParser when bullet collision library is found
Add Newton's cradle app (need more work)
Set default restitution coefficient for BodyNode to 0
Fix incorrect use of macro in ContactConstraint.cpp
Decrease default maximum error reduction velocity from 1e+1 to 1e-3
Add Newton's cradle app (need more work) (reverted from commit 383acb507c47dd4d371d2a9a20d3976dcb2fcccf)
Fix bug in updating transmitting wrench at BodyNode::updateConstrainedTransmittedForce()
Declare conflict on libdart-core3-dev
Merge pull request #203 from j-rivero/release-4.0

Thanks, Jose!
Remove unnecessary header inclusion in BodyNode.h

This resolve compiler error when DART failed to find any installed optimization library.
Merge branch 'release-4.0'