Split `build.sh` into separately-executable steps.

[mikewest]

Currently, build.sh does everything every time. It would be lovely if we could at least split component updates (caniuse, unicode, etc) from the actual spec generation process such that they could be executed independently. There's no reason to require network access for spec generation, and hitting the network significantly slows things down.

[sideshowbarker]

#13 effectively splits out the network-requiring steps in such a way that you can skip them by specifying the --no-update switch. Beyond that I don’t know what more splitting out of steps we might want to do; I think there are maybe a couple more places to get more granular on what you can optionally skip, but that said I’m not sure it would be worth the effort to go any further at this point at least. I certainly don’t think it’d buy much time, because when I run with --no-update on my laptop (OS X Macbook) environment right now, the build completes in around 14 seconds.

[domenic]

Yeah. 15 seconds on my Thinkpad, using the remote build server. Anything left to do here?

[sideshowbarker]

Nothing left to do here afaict. But would like to confirm that @mikewest is satisfied.

[mikewest]

Sure.