Add CI with Github Actions

Check for compatibility with all version of Emacs since Emacs 25.1

Add Cask file for managing dependencies in CI

Add badge in README for CI

Makefile

@@ -0,0 +1,11 @@
+# -*- indent-tabs-mode: t -*-
+
+export EMACS ?= $(shell which emacs)
+CASK ?= $(shell which cask)
+
+all: compile
+
+compile:
+	${CASK} exec ${EMACS} -Q --script bin/compile-package.el 2>&1 | grep -A 2 -E "([Ee]rror|[Ww]arning):" && exit 1 || exit 0
+
+.PHONY: all compile