Add haskell module

This module provides support for per user haskell packages by prepending
the per user directories to PATH/MANPATH.

modules/haskell/README.md

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+Haskell
+=======
+
+Enables local Haskell package installation.
+
+Per-user Package Installation
+-----------------------------
+
+[Cabal][1], the Haskell package manager, can install packages into per user
+directories.
+
+This module prepends per user directories to the relevant path variables to
+enable the execution of user installed executables and the reading of
+documentation.
+
+### Usage
+
+Install packages into per user directories with `cabal install --user`.
+
+Authors
+-------
+
+*The authors of this module should be contacted via the GitHub issue tracker.*
+
+ - [Sebastian Wiesner](/lunaryorn)
+
+[1]: http://www.haskell.org/cabal/
+

modules/haskell/init.zsh

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+#
+# Enables local Haskell package installation.
+#
+# Authors:
+#   Sebastian Wiesner <lunaryorn@googlemail.com>
+#
+
+# Prepend Cabal per user directories to PATH/MANPATH.
+if [[ "$OSTYPE" == darwin* ]]; then
+  path=($HOME/Library/Haskell/bin(/N) $path)
+  manpath=($HOME/Library/Haskell/man(/N) $manpath)
+else
+  path=($HOME/.cabal/bin(/N) $path)
+  manpath=($HOME/.cabal/man(/N) $path)
+fi
+