Simplify file reading and writing
Post and Pre Processor updates

- optional image path conversion to absolute, base64, or not at all
- optional file path conversion to absolute or not at all
- optional multimarkdown critic marks can be stripped (accepted or
rejected)
Don't add file:// if not already there
Account for windows specific paths
- filter out paths that start with drive letters
- if a leading "\" on windows can makes it to the absolute parser filter it out
Patch b64 absolute path logic
Make sure the calculated abspath exists
Merge pull request #203 from facelessuser/master

Preprocessor and Postprocessor changes