Markdown-ify README and add Travis-CI script

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

.travis.yml

+env:
+ - GHCVER=7.4.1
+ - GHCVER=7.4.2
+ - GHCVER=7.6.1
+ - GHCVER=7.6.2
+ - GHCVER=7.6.3
+
+before_install:
+ - sudo add-apt-repository -y ppa:hvr/ghc
+ - sudo apt-get update
+ - sudo apt-get install cabal-install-1.18 ghc-$GHCVER autoconf
+ - export PATH=/opt/ghc/$GHCVER/bin:$PATH
+
+install:
+ - cabal-1.18 update
+ - ghc --version
+
+script:
+ - autoreconf -i
+ - cabal-1.18 configure -v2
+ - cabal-1.18 build
+ - cabal-1.18 check
+ - cabal-1.18 sdist

README

-To build this package using Cabal directly from darcs, you must run
-"autoreconf" before the usual Cabal build steps (configure/build/install).
-autoreconf is included in the GNU autoconf tools.  There is no need to run
-the "configure" script: the "setup configure" step will do this for you.

README.md

+The `unix` Package  [![Build Status](https://travis-ci.org/ghc/packages-unix.png?branch=master)](https://travis-ci.org/ghc/packages-unix)
+==================
+
+See [`unix` on Hackage](http://hackage.haskell.org/package/unix) for
+more information.
+
+Installing from Git
+-------------------
+
+To build this package using Cabal directly from Git, you must run
+`autoreconf -i` before the usual Cabal build steps (`cabal
+{configure,build,install}`). The program `autoreconf` is part of
+[GNU autoconf](http://www.gnu.org/software/autoconf/).  There is no
+need to run the `configure` script: `cabal configure` will do this for
+you.