CHM style fixes

Updated css to use theme-base and theme-medium from php.net and google
fonts.
New stylesheet references have been placed in the phd config.php
Separated stylesheet loading and rendering into ChunkedXHTML methods.
Standardised process between CHM and Epub.
Add a few css tweaks to sort out the new style in CHM.
Bugfix in Format.php for non-existant array key.
Tested with epub and chm rendering under php 5.5.10 on win 8.1
Reverted Format.php

Format.php unmodified
Merge pull request #8 from andyburton/master

CHM style fixes

* andyburton/master:
  Reverted Format.php
  CHM style fixes
Fixed bug#66408 (Wrong style file in chm documentation). (Andy Burton)