Move the build support scripts for travis to a hidden
subdirectory to keep the top level directory more
clean.

Remove unnecessary python3 environment from osx that
made configuring the test environment slower.

Use "addon:" features for installing homebrew
packages more efficiently.

Re-organized the .travis.yml file in a standard
order so that the "before-install" and "install"
steps occur after the configurations of addons and
 matrix, and language features are set.

Drop gcc b/c it takes too long to install via addon.

Build only static/release, to save VMs. (No shared to debug.)