Motivation for this change

We're trying to write a make2nix utility at Awake Networks, but due to the complexity of
Make's semantics we'd like to reuse the kati project to transform Makefiles to the simpler
ninja file format which we can then more easily translate to Nix derivations

The first step in this is adding kati to nixpkgs, which is what this change does

NOTE: This does not build on master most likely due to changes introduced in 6b999f3 which break the following chain of derivations:

  /nix/store/4dsy1vkny9938yqg5k5c3lg357v2dzha-python2.7-hypothesis-3.11.0.drv
  /nix/store/qp1dwblvm3wn4xq3x59rcz9ncaphhm2b-python2.7-cryptography1.8.1.drv
  /nix/store/dg59z5r33nrlm3622nan403zb7qj3zfn-python2.7-paramiko-2.1.1.drv
  /nix/store/4fz077qbsw2b6xvp7csmdyhbxikpj2bm-bazaar-2.7.0.drv
  /nix/store/c7p5sbpan0qa45n9x8gsnkqh9k32q969-go-1.8.3.drv
  /nix/store/jqf40zx08bkbz0zrsz8vx1v6f0masiy8-govers-20150109-3b5f175.drv
  /nix/store/m05bhn2c0bx4pwgl944a4njz58jrvkw6-kati-unstable-2017-05-23.drv

... but this does build on a fairly recent commit (4cbd5e4) so once the Python-related breakage is fixed this build should succeed again

cc: @taktoa (who is also using this to write a haskell2nix utility for incremental Haskell builds
by taking advantage of GHC's Makefile output)

Things done

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.