Fixing blockquotes and refactoring

Blockquotes are fixed. Rather than hacking on the marshaler, I am
populating a secondary struct with raw XML. The standard marshaler is
able to work with this struct perfectly.

The code has been refactored. All of the (un)?marshaling structs and
implementations have been moved to domain-specific files. Helper
functions are defined so that data is stored in an intermediary slice
and map. The program is still just dumping that data to STDOUT, but all
the hard work for a higher level functionality is done.

Structure for test documents

Initial commit

Parses an EPUB archive into HTML. Currently dumps everything to STDOUT,
but can push into array and then sort according to table of contents.

Blockquotes are not handled correctly. Need to hack on (un)marshaler for
that to work correctly.

Titles are not always handled correctly. Need to look for more than just
h3 tags (i.e. h1, h2) and need to let these bubble up from div tags.