Add spark package

packages/spark.rb

+require 'package'
+
+class Spark < Package
+  description 'sparklines for your shell'
+  homepage 'https://zachholman.com/spark/'
+  version 'ab88ac'
+  source_url 'https://raw.githubusercontent.com/holman/spark/ab88ac6f8f33698f39ece2f109b1117ef39a68eb/README.md'
+  source_sha256 '85a153beeafea5637615644f2e92e47e71c621ffa1b0d995acadf51d1c9bbd0d'
+
+  def self.install
+    system 'wget https://raw.githubusercontent.com/holman/spark/ab88ac6f8f33698f39ece2f109b1117ef39a68eb/spark'
+    abort 'Checksum mismatch. :/ Try again.'.lightred unless Digest::SHA256.hexdigest( File.read('spark') ) == '1fa0ef384309239f27f8c98c843639cac2c59e4fe51413cca9836ea64f73329d'
+    system "install -Dm755 spark #{CREW_DEST_PREFIX}/bin/spark"
+  end
+end