First stab at new gem/binary integration

It's not hooked up yet, but we can now build a gem that installs an
`overcommit` binary. That binary uses the newly-created Overcommit::CLI
class, whose implementation is strikingly similar to that of
`scss-lint`. I think Shane did a great job architecting that project, so
I'll be following many of the same patterns.

Change-Id: I9a2d7bc9c042e5c28385bca3647e4c9e4491350f
Reviewed-on: https://gerrit.causes.com/22314
Tested-by: Aiden Scandella <aiden@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>

Author: Aiden Scandella

bin/overcommit

@@ -0,0 +1,11 @@
+#!/usr/bin/env ruby
+
+$: << File.expand_path('../../lib', __FILE__)
+
+require 'overcommit'
+require 'overcommit/cli'
+
+Overcommit::CLI.new(ARGV).tap do |cli|
+  cli.parse_arguments
+  cli.run
+end

lib/overcommit.rb

@@ -0,0 +1 @@
+require 'overcommit/version'

lib/overcommit/cli.rb

@@ -0,0 +1,47 @@
+require 'optparse'
+
+module Overcommit
+  class CLI
+
+    def initialize(arguments = [])
+      @arguments = arguments
+      @options   = {}
+    end
+
+    def parse_arguments
+      parser = OptionParser.new do |opts|
+        opts.banner = "Usage: #{opts.program_name} [options] target"
+
+        opts.on_tail('-h', '--help', 'Show this message') do
+          print_help opts.help
+        end
+
+        opts.on_tail('-v', '--version', 'Show version') do
+          puts VERSION
+          exit 0
+        end
+      end
+
+      begin
+        parser.parse!(@arguments)
+
+        # Unconsumed arguments are our targets
+        @options[:targets] = @arguments
+      rescue OptionParser::InvalidOption => ex
+        print_help parser.help, ex
+      end
+    end
+
+    def run
+      raise NotImplementedError, 'Nothing to see here yet'
+    end
+
+  private
+
+    def print_help(message, ex = nil)
+      puts ex, '' if ex
+      puts message
+      exit 0
+    end
+  end
+end

lib/overcommit/version.rb

@@ -0,0 +1,3 @@
+module Overcommit
+  VERSION = '0.1.0'
+end

overcommit.gemspec

@@ -0,0 +1,22 @@
+$: << File.expand_path('../lib', __FILE__)
+require 'overcommit/version'
+
+Gem::Specification.new do |s|
+  s.name              = 'overcommit'
+  s.version           = Overcommit::VERSION
+  s.license           = 'MIT'
+  s.date              = '2013-05-15'
+
+  s.summary     = 'Opinionated git hook manager'
+  s.description = 'Overcommit is a utility to install and extend git hooks'
+
+  s.authors  = ['Causes Engineering']
+  s.email    = 'eng@causes.com'
+  s.homepage = 'http://github.com/causes/overcommit'
+
+  s.require_paths = %w[lib]
+
+  s.executables = ['overcommit']
+
+  s.files = `git ls-files -- lib`.split("\n")
+end