Adding skeletal changelog and contributing .md files; not done yet.
Deleted the old ChangeLog.txt which was way out of date.
Filling out CONTRIBUTING.md; still not done.
Update CONTRIBUTING.md

Fix TOC.
Filled in 3.5 changelog section.
Merge branch 'master' of https://github.com/simbody/simbody
Moved the CLA terms to the end in an attempt to be friendlier in tone.
Back-filled 3.3.1 changelog.
Update CONTRIBUTING.md

Minor edits.
Try /maxcpucount:4 and --parallel 4

Was just /maxcpucount; not sure what that does and test were run 8 at a time.
Add AppVeyor build status badge.
Merge branch 'master' into cmaes-mpi