Sorted out mime initialization.

Every mime related function in main __init__.py has a flag check for the
check if initialization has already done. This is nonsense, since it
should be done implicitly early on the converter is starting.

This commit straight the things out, and initialization is done in cli
module.

Also, function guess_type was removed, since it's just a proxy for
mimetypes.guess_type function.

ebook_converter/ebooks/docx/to_html.py

@@ -1,5 +1,6 @@
 import sys, os, re, math, errno, uuid, numbers
 from collections import OrderedDict, defaultdict
+import mimetypes
 
 from lxml import etree
 from lxml import html
@@ -24,8 +25,6 @@ from ebook_converter.ebooks.metadata.opf2 import OPFCreator
 from ebook_converter.utils.localization import canonicalize_lang, lang_as_iso639_1
 
 
-__license__ = 'GPL v3'
-__copyright__ = '2013, Kovid Goyal <kovid at kovidgoyal.net>'
 
 NBSP = '\xa0'
 
@@ -384,7 +383,7 @@ class Convert(object):
         opf.create_manifest_from_files_in([self.dest_dir])
         for item in opf.manifest:
             if item.media_type == 'text/html':
-                item.media_type = guess_type('a.xhtml')[0]
+                item.media_type = mimetypes.guess_type('a.xhtml')[0]
         opf.create_spine(['index.html'])
         if self.cover_image is not None:
             opf.guide.set_cover(self.cover_image)