Adding CLI argument template

In v0.5, the Mustache template is hardcoded as
`./lib/rocco/layout.mustache`.  This makes it quite difficult to
style generated content as one must edit the layout file inside the
gem itself to make changes.

I propose leaving that file as a sensible default, but allowing the user
to specify an absolute or relative (to the current working directory)
path to a mustach template of her choosing.  That's implemented in this
commit.

bin/rocco

@@ -7,6 +7,7 @@
 #/   -c, --comment-chars=<chars>
 #/                          The string to recognize as a comment marker
 #/   -o, --output=<dir>     Directory where generated HTML files are written
+#/   -t, --template=<path>  The file to use as template when rendering HTML
 #/       --help             Show this help message
 
 require 'optparse'
@@ -37,6 +38,7 @@ ARGV.options { |o|
   o.on("-o", "--output=DIR") { |dir| output_dir = dir }
   o.on("-l", "--language=LANG") { |lang| options[:language] = lang }
   o.on("-c", "--comment-chars=CHARS") { |chars| options[:comment_chars] = Regexp.escape(chars) }
+  o.on("-t", "--template=TEMPLATE") { |template| options[:template_file] = template }
   o.on_tail("-h", "--help") { usage($stdout, 0) }
   o.parse!
 } or abort_with_note

lib/rocco.rb

@@ -82,10 +82,12 @@ class Rocco
     defaults = {
       :language      => 'ruby',
       :comment_chars => '#',
+      :template_file => nil
     }
     @options = defaults.merge(options)
     @sources = sources
     @comment_pattern = Regexp.new("^\\s*#{@options[:comment_chars]}")
+    @template_file = @options[:template_file]
     @sections = highlight(split(parse(@data)))
   end
 
@@ -102,10 +104,14 @@ class Rocco
   # for building an index of other files.
   attr_reader :sources
 
+  # An absolute path to a file that ought be used as a template for the
+  # HTML-rendered documentation.
+  attr_reader :template_file
+
   # Generate HTML output for the entire document.
   require 'rocco/layout'
   def to_html
-    Rocco::Layout.new(self).render
+    Rocco::Layout.new(self, @template_file).render
   end
 
   #### Internal Parsing and Highlighting

lib/rocco/layout.rb

@@ -3,8 +3,11 @@ require 'mustache'
 class Rocco::Layout < Mustache
   self.template_path = File.dirname(__FILE__)
 
-  def initialize(doc)
+  def initialize(doc, file=nil)
     @doc = doc
+    if not file.nil?
+      Rocco::Layout.template_file = file
+    end
   end
 
   def title