This PR makes a few changes to how things are done:
a) build and install "koch" - the nim make-type tool
b) use "koch" to bootstrap nim
c) build additional supporting tools such as nimble, nimgrep and nimsuggest
d) nim can use other c compilers than gcc, so instead of forcing gcc we use the one from stdenv
e) run the full test suite
We do not need the "nimble" package any longer as it is part of nim.
I've removed the trivial command in 4e72b61de.
I think `install -Dt "$out/bin"` is a better replacement anyway,
as it can be easily used to other directories than $out/bin.
/cc @ehmry who seems to maintain many packages with this usage.
(BTW, it would be better to have maintainer attribute same as github
username, as it makes pinging maintainers much easier.)
