add link shortening option

This commit gives jist the new ability to shorten gist URLs using
GitHub's URL shortener, git.io. It adds two options on the command
line (`-s` and `--shorten`).

If the shortening step fails, or if git.io is down, jist will just
return the normal, unshortened version.

bin/jist

@@ -29,6 +29,9 @@ Anonymous gists are not associated with your GitHub account, they can be created
 with "-a" even after you have used "jist --login". If you already have an access
 token with the "gist" scope, you can pass that with "-t".
 
+If you would like to shorten the resulting gist URL, use the -s flag. This will
+use GitHub's URL shortener, git.io.
+
 To copy the resulting URL to your clipboard you can use the -c option, or to just
 open it directly in your browser, use -o. You can add `alias jist='jist -c'` to
 your shell's rc file to configure this behaviour by default.
@@ -37,7 +40,7 @@ Instead of creating a new jist, you can update an existing one by passing its ID
 or URL with "-u". For this to work, you must be logged in, and have created the
 original gist with the same GitHub account.
 
-Usage: #{executable_name} [-o|-c] [-p] [-d DESC] [-t TOKEN|-a] [-u URL] [-P] [-f NAME]* FILE*
+Usage: #{executable_name} [-o|-c] [-p] [-s] [-d DESC] [-t TOKEN|-a] [-u URL] [-P] [-f NAME]* FILE*
        #{executable_name} --login
 
   EOS
@@ -68,6 +71,10 @@ Usage: #{executable_name} [-o|-c] [-p] [-d DESC] [-t TOKEN|-a] [-u URL] [-P] [-f
     options[:anonymous] = true
   end
 
+  opts.on("-s", "--shorten", "Shorten the gist URL using git.io.") do |shorten|
+    options[:shorten] = shorten
+  end
+
   opts.on("-t", "--token OAUTH_TOKEN", "The OAuth2 access_token to use.") do |token|
     options[:access_token] = token
   end

lib/jist.rb

@@ -28,6 +28,7 @@ module Error; end
   # @option options [String] :filename  ('a.rb') the filename
   # @option options [Boolean] :public  (false) is this gist public
   # @option options [Boolean] :anonymous  (false) is this gist anonymous
+  # @option options [Boolean] :shorten  (false) Shorten the resulting URL using git.io.
   # @option options [String] :access_token  (`File.read("~/.jist")`) The OAuth2 access token.
   # @option options [String] :update  the URL or id of a gist to update
   # @option options [Boolean] :copy  (false) Copy resulting URL to clipboard, if successful.
@@ -50,6 +51,7 @@ def gist(content, options = {})
   # @option options [String] :description  the description
   # @option options [Boolean] :public  (false) is this gist public
   # @option options [Boolean] :anonymous  (false) is this gist anonymous
+  # @option options [Boolean] :shorten  (false) Shorten the resulting URL using git.io.
   # @option options [String] :access_token  (`File.read("~/.jist")`) The OAuth2 access token.
   # @option options [String] :update  the URL or id of a gist to update
   # @option options [Boolean] :copy  (false) Copy resulting URL to clipboard, if successful.
@@ -91,7 +93,12 @@ def multi_gist(files, options={})
     begin
       response = http(request)
       if Net::HTTPSuccess === response
-        on_success(response.body, options)
+        response = on_success(response.body, options)
+        if options[:shorten]
+          {'html_url' => shorten(response['html_url'])}
+        else
+          response
+        end
       else
         raise "Got #{response.class} from gist: #{response.body}"
       end
@@ -105,6 +112,20 @@ def multi_gist(files, options={})
     raise e.extend Error
   end
 
+  # Given a URL, shorten it
+  #
+  # Based on https://gist.github.com/1762136
+  def shorten(url)
+    response = Net::HTTP.post_form(URI("http://git.io/"), :url => url)
+    case response.code
+    when "201"
+      response['Location']
+    else
+      # If the shortener failed, just return the unshortened URL.
+      url
+    end
+  end
+
   # Log the user into jist.
   #
   # This method asks the user for a username and password, and tries to obtain