Add build.sh for building on Posix platforms

build.sh

+#!/bin/bash -e
+
+root=`dirname $0`
+mkdir -p $root/_shake
+ghc --make -Wall $root/src/Main.hs -i$root/src -rtsopts -with-rtsopts=-I0 -outputdir=$root/_shake -o $root/_shake/build
+$root/_shake/build --lint --directory $root/.. $@