Add Docker script to use for Linux build

.dockerignore

@@ -0,0 +1,3 @@
+**/.stack-work
+release
+test

Dockerfile

@@ -0,0 +1,6 @@
+FROM ubuntu:14.04
+# needed for final Haskell linking
+# (these are installed by stack script but we're not doing that)
+RUN apt-get update && apt-get -y install g++ libgmp-dev
+# needed for Stack to unpack GHC
+RUN apt-get update && apt-get -y install make xz-utils

Makefile

@@ -1,12 +1,22 @@
 version := $(shell release/version)
 
-.PHONY: build
+.PHONY: build docker
 
 build:
 	stack build
 	rm -rf release/${version} release/${version}.zip
 	mkdir release/${version}
-	cp $(shell stack exec which pokemid) release/${version}/
+	stack exec which pokemid | xargs -I{} cp {} release/${version}/
+	strip release/${version}/pokemid*
+	cp README.md release/${version}/README.txt
+	cd release && zip -r ${version}.zip ${version}
+
+docker:
+	docker build -t onyxite/pokemid .
+	stack --docker --docker-image=onyxite/pokemid build
+	rm -rf release/${version} release/${version}.zip
+	mkdir release/${version}
+	stack --docker --docker-image=onyxite/pokemid exec which pokemid | xargs -I{} cp {} release/${version}/
 	strip release/${version}/pokemid*
 	cp README.md release/${version}/README.txt
 	cd release && zip -r ${version}.zip ${version}

README.md

@@ -46,8 +46,9 @@ should work as well as long as you also have [GHC], [Alex], and [Happy].
 [Happy]: https://www.haskell.org/happy/
 [Cabal]: https://www.haskell.org/haskellwiki/Cabal-Install
 
-`make` uses Stack to produce a release `.zip` file.
-Ruby is also used to get the package version.
+`make` uses Stack to produce a release `.zip` file. Ruby is also required to get
+the package version. `make docker` uses Docker to build in an older Linux
+distribution for higher compatibility.
 
 ## Usage