Allow all Formatters to accept options hash

None of the built in formatters yet do anything with these options. However, it
provides a consistent #initialize API that allows us to promote "formatter
options" as a concept further up the stack in Capistrano.

For example, in Capistrano we can offer this configuration system:

set :format, ...
set :format_options, key: value, ...

We can only reasonable offer this if we are sure that the underlying formatters
all accept an options hash (i.e. the :format_options).

Most importantly, Airbrussh *does* have options, and this will allow us to have
a standard way for those options to be declared. Airbrussh will be the default
formatter in a future version of Capistrano, and this commit is part of laying
the groundwork.

CHANGELOG.md

@@ -13,6 +13,8 @@ appear at the top.
   * display more accurate string for commands with spaces being output in `Formatter::Pretty`
     [PR #304](https://github.com/capistrano/sshkit/pull/304)
     @steved
+  * `SSHKit::Formatter::Abstract` now accepts an optional Hash of options
+    [PR #308](https://github.com/capistrano/sshkit/pull/308) @mattbrictson
 
 ## 1.8.1
 

lib/sshkit/formatters/abstract.rb

@@ -7,12 +7,13 @@ module Formatter
     class Abstract
 
       extend Forwardable
-      attr_reader :original_output
+      attr_reader :original_output, :options
       def_delegators :@original_output, :read, :rewind
       def_delegators :@color, :colorize
 
-      def initialize(output)
+      def initialize(output, options={})
         @original_output = output
+        @options = options
         @color = SSHKit::Color.new(output)
       end