Add sccache to CI builds

[kjvalencik]

CI builds are fairly slow because of the large number of projects. However, since most projects use the same set of dependencies, sccache should give a significant speed-up.

[kjvalencik]

I'm also working on getting workspaces functioning correctly. After that lands, making all the examples members of a workspace should improve build time.

https://github.com/kjvalencik/neon/tree/workspaces