Emit more compiler warnings

[KristianLyng]

There are a whole buck-load more compiler warnings we could emit. I am adding this as a TODO-item because I want to fix the warnings we have before I add more warnings. See #12 for that.

[KristianLyng]

I did a dry-run of this today with my now-usual set of warnings, and unsurprisingly there were two major sinners:

const-correctness (we actually got a patch for this in beryl, but because it was mindboggingly huge and from an unkown, we didn't accept it). This is largely about option-stuff that's easily fix.

unused parameters - this is what we get for tons of generic interfaces. Some of it should probably be fixed.

In addition to that there were a set of shadowed variables I resolved. These are mostly a result of really bad code practices (huge functions, global variables, copy/paste).