added headers and footers to docx

Grab from this PR: ruby-docx#153

lib/docx/document.rb

@@ -22,7 +22,7 @@ module Docx
   class Document
     include Docx::SimpleInspect
 
-    attr_reader :xml, :doc, :zip, :styles
+    attr_reader :xml, :doc, :zip, :styles, :headers, :footers
 
     def initialize(path_or_io, options = {})
       @replace = {}
@@ -40,6 +40,8 @@ def initialize(path_or_io, options = {})
 
       @document_xml = document.get_input_stream.read
       @doc = Nokogiri::XML(@document_xml)
+      @headers = fetch_headers
+      @footers = fetch_footers
       load_styles
       yield(self) if block_given?
     ensure
@@ -75,6 +77,20 @@ def bookmarks
       bkmrks_hsh
     end
 
+    def fetch_headers
+      @zip.glob('word/header*.xml').map do |entry|
+        header_xml = entry.get_input_stream.read
+        Nokogiri::XML(header_xml)
+      end
+    end
+
+    def fetch_footers
+      @zip.glob('word/footer*.xml').map do |entry|
+        footer_xml = entry.get_input_stream.read
+        Nokogiri::XML(footer_xml)
+      end
+    end
+
     def to_xml
       Nokogiri::XML(@document_xml)
     end
@@ -210,6 +226,12 @@ def load_rels
     def update
       replace_entry 'word/document.xml', doc.serialize(save_with: 0)
       replace_entry 'word/styles.xml', styles_configuration.serialize(save_with: 0)
+      headers.each_with_index do |header, index|
+        replace_entry "word/header#{index + 1}.xml", header.serialize(:save_with => 0) if header
+      end
+      footers.each_with_index do |footer, index|
+        replace_entry "word/footer#{index + 1}.xml", footer.serialize(:save_with => 0) if footer
+      end
     end
 
     # generate Elements::Containers::Paragraph from paragraph XML node
@@ -226,4 +248,4 @@ def parse_table_from(t_node)
       Elements::Containers::Table.new(t_node)
     end
   end
-end
+end