Merge pull request #3 from simbody/master

Updating my master branch.
[appveyor] Build as 64bit.
Merge pull request #277 from chrisdembia/appveyor-64

[appveyor] build as 64bit.
[readme] Appveyor badge points to master branch.
Merge pull request #278 from chrisdembia/readme-appveyor-status-master

[readme] Appveyor badge points to master branch.
[appveyor] Don't nupkg for pull requests.
Fill in missing changes to older releases.
Merge branch 'master' of https://github.com/simbody/simbody
Filled in some of the coding standards section.
Merge pull request #279 from chrisdembia/appveyor-nuget-l

[appveyor] Don't nupkg for pull requests.
Make fixes suggested by @chrisdembia.
Trivial change just to kick off a build.
In preparation for rejecting files with tabs in them, fix all the old Simbody files that contain tabs.
I replaced each tab with four spaces; this will cause formatting problems in some places.
Merge pull request #281 from simbody/contributing-md

[WIP] Fill in CONTRIBUTING.md instructions
[travis] Fail if tabs found in CMake, cpp, c, h.
Merge pull request #282 from simbody/getRidOfAllTabs

Get rid of all tabs
[travis] Apply @sherm1's stringent no-tabs policy.

More filetypes now need to obey no-tabs policy: .md .yml .cmake .xml .html .in
[travis] Test for tabs before all else.
[travis] no-tab check had redundant CMakeLists.txt
[travis] only perform no-tab check on linux.