Travis build timeouts

[dennissergeev]

Description

(Discussion started in #180)

@sit I can tweak the Travis config to allow for a longer build.

In the long-term, however, it's worth to look into optimising the build process or splitting into chunks somehow (compiling RRTM separately?).

In terms of optimising the compilation, perhaps we can change some flags and do a "quick and dirty" compilation on Travis?

[sit23]

Thanks @dennissergeev - I agree that this is definitely worth thinking about. Looking at ways of making the compilation faster using flag changes on Travis would be useful, but would perhaps then create different circumstances for testing and use, which might prove tricky.

I agree that it might be possible to chunk RRTM a bit more - e.g. it's possible that we're compiling more of RRTM than we need to, and a few well-placed ifdef statements could make its compilation much faster.

I'll have a think about this.