guarantee that ragdoll is clear before initialized
remove unecessary clearRagdollConstraintsAndPoints()
Merge pull request #3096 from AndrewMeadows/bug-fix

fix for assert crash in SkeletonModel::initRagdollPoints()
update BUILD.md to remove zlib requirement
Merge branch 'master' of https://github.com/highfidelity/hifi into metavoxels