Update manuals for 3.8 release (#823)

* Minor updates for 3.8

* README & CONTRIBUTING updates

Prep release 3.7 (#680)

Update location of doxygen; prepare for 3.7 release.

This patch release is 3.6 with minor changes:

- Fixed a bug wherein a program may crash when using the visualizer if
  the visualizer window was closed manually.

Simbody release 3.6

This is the first release of Simbody that requires C++11, as much of the
code base now takes advantage of C++11 features. The MinGW compiler is
now supported, providing an alternative to Visual C++ on Windows. This
release fixes a bug in MultibodyGraphMaker where massless bodies were
handled incorrectly. The state's caching mechanism is now more
fine-grained ("stage versions"), though this change should not affect
users in this release.

If upgrading from 3.5, you may need to make minor changes to downstream
code:

- SimTK::ClonePtr's equality comparison operator previously checked
  equality between the underlying objects, but now checks equality between
  pointers.
- Support for long double has been removed.
  Some methods in SimTK::ClonePtr and SimTK::ReferencePtr have been
  renamed.
- SimTK::Xml was changed from a class to a namespace.
- Where possible, we have deprecated previous methods rather than removing
  them completely.

There were numerous smaller improvements to Simbody since the previous
release, in build and installation, documentation, performance, bug
fixes, and small enhancements. For details, see CHANGELOG.md.

For installation instructions, see README.md.
For API documentation, see
https://simbody.github.io/simbody-3.6-doxygen/api/.
For information on contributing to the Simbody project, see
CONTRIBUTING.md.

If you have questions or problems, please post to the Simbody Forum.

This patch release is 3.5.3 with minor changes:

- The source will now compile on macOS with Xcode 8 and SDK MacOSX10.12.sdk.

Update readme to reflect version 3.5.3

Update CHANGELOG to include 3.5.2, fix version numbers in README.

Updated to use 3.5.1 in examples rather than 3.5

[ci skip]

Change release date.

[ci skip]

Merge pull request #133 from j-rivero/simbody-3.4

Update debian metadata for simbody 3.4