Clean up the code base to follow a style guide
This normalizes a number of things within the codebase. Mostly:
- lines are now at most 80 characters
- indentation should now be consistently 4 spaces
This should hold for all files except src/*/Examples.hs
, which are left untouched as we do not know yet what to do with them.
As suggested 'offline', I propose that we now follow roughly the Futhark style guide when contributing.
There are a few additional simple rewrites in this MR (which in principle are separated into other commits atm). Do feel free to squash everything if/when you merge.