fix(install): use prepublish script rather than install

scripts/install.js requires lodash (and other modules), but if they are
direct dependencies of an application then they may not be available
when the `install` step runs in npm.

Convert from running the script as an `install` script to a `prepublish`
script so that other application dependencies are available at the time
it runs.

Closes #37
optional readyFile suffix
Merge pull request #38 from stu-salsbury/prepublish-for-install

fix(install): use prepublish script rather than install
release 0.7.1
Merge pull request #41 from geekdave/readyfile-suffix

optional readyFile suffix
updated changelog
fixing lint errors
release 0.8.0
#38 changed prepublish to postinstall
release 0.8.1
always ignore sc/ directory
updating changelog
release 0.8.2
bumping default sc version
release 0.9.0
udpated change log
adding ALL THE BADGES
Factor downloading out to minimize load-time dependencies

This works around (what appears to be) a npm bug during installation:
https://github.com/npm/npm/issues/6624