Allow `mason install` to work without scripts?

I'm pondering the best, most lightweight, method to recommend installing mason packages on CI systems.

Installing mason with git clone -b master --single-branch https://github.com/mapbox/mason.git brings down > 2.7 MB of data and this will likely grow over time.

That is not a lot, but much more than is needed to install a package, which can currently be done as simply as:

PACKAGE_URL="https://mason-binaries.s3.amazonaws.com/${TRAVIS_OS_NAME}-x86_64/${MASON_NAME}/${MASON_VERSION}.tar.gz"
travis_retry wget --quiet -O - ${PACKAGE_URL} | tar -xz

For packages representing libraries most usecases will want/need the main mason command in order to query for cflags and ldflags. But for command line tools these features are unnecessary.

Two ideas (with command line tools in mind):

• Write a very small mason-install script that CI systems could download and use to install a package: ./mason-install clang 3.8.0. It would not work for header-only libs (would put them in the wrong location)
• Modify the existing mason binary to work for installs without needing the script/ metadata around.
  • This would require disabling the checks for MASON_LIB_FILE among other modifications. Hmmmm...

/cc @ericfischer @TheMarex (maintainers on two repos that are using the manual method to install, but this is brittle)

Start by inspecting the existing mason binary and the script/ metadata checks mentioned in the issue. Compare the proposed standalone mason-install script with changing the binary to install without metadata, including the stated header-only library limitation. The issue does not name files or tests, and completion criteria would need to be defined.