refactor: create nix folder

Author: nokome

.travis.yml

@@ -7,6 +7,6 @@ script:
   # There does not appear to be an option to turn this off so redirect it to file.
   # Travis will also kill a build if no output is received for 10 mins, so
   # use `travis_wait` to ensure that does not happen.
-  - (cd pkgs/development/node-packages; travis_wait 60 ./generate.sh)
-  - (cd pkgs/development/python-modules; ./generate.sh)
-  - (cd pkgs/development/r-modules; ./generate.sh)
+  - (cd nix/pkgs/development/node-packages; travis_wait 60 ./generate.sh)
+  - (cd nix/pkgs/development/python-modules; ./generate.sh)
+  - (cd nix/pkgs/development/r-modules; ./generate.sh)

lib/maintainers.nix renamed to nix/lib/maintainers.nix

@@ -0,0 +1,4 @@
+R script to
+Based on https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/r-modules/generate-r-packages.R
+
+`default.nix` and `generate-r-packages.R` are from the upstream folder (pkgs/development/r-modules)[https://github.com/NixOS/nixpkgs/tree/master/pkgs/development/r-modules]

pkgs/applications/science/biology/psmc/default.nix renamed to nix/pkgs/applications/science/biology/psmc/default.nix

@@ -0,0 +1,11 @@
+#! /usr/bin/env nix-shell
+#! nix-shell -i bash -p wget parallel R rPackages.data_table
+#! nix-shell -I nixpkgs=../../..
+
+# Generate new `*-packages.nix` files for each R package repository
+# in the following list. 
+# The renaming step is required because `generate-r-packages.R <repo>` reads `<repo>-packages.nix`
+for repo in cran bioc bioc-annotation bioc-experiment; do
+    Rscript generate-r-packages.R $repo > $repo-packages.nix.new
+    [ -s $repo-packages.nix.new ] && mv $repo-packages.nix.new $repo-packages.nix
+done