Log Message:
Initial import of epubpreflight-0.1.0:

epubpreflight is a tool for checking ePub files. It does not do
validation, that is the role of the epubcheck tool. The epubpreflight
tool is intended to check the things that are not mentioned in the
EPUB spec, but that could be issues in one environment or another.

The things that epubpreflight currently gives errors for are:
* Content files that are empty.
* Content files that are over 300KB.
* Image files that are empty.
* Image files that are over 10MB.

It doesn't yet check the stylesheets.