Merge pull request #14 from dartsim/master

Fix bug: sphereSphereIntersect calculates wrong contact point
fix some bug in gjk; add continuous collision, still need more test
penetration depth
penetration depth
penetration depth
vec nf
remove bug in cmake
fix cmake bug
fix the xml data
fix the compiling problem in windows
fix a bug in xmldata
add new data for PD and fix some bugs
make pd deterministic
make pd deterministic