Fix #8: If a file's mtime is before 1980, set the mtime to "right now".

Fix #4: Use the local file system's encoding to decode the byte
string received when reading the file's contents.

Change cover image detection to include tags that may only start
with "cover".

Implement a patch submitted on bug #1. Change patch to avoid looping by
taking advantage of some assumptions that the ePub specification and XML
rules suggest are valid. This should be the primary method of detecting
the cover image, falling back to the previous method of scanning the
manifest only if no cover image can be found.