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/oeb/transforms/flatcss.py

@@ -3,6 +3,7 @@ CSS flattening transform.
 """
 import collections
 import math
+import mimetypes
 import numbers
 import operator
 import re
@@ -13,7 +14,6 @@ import css_parser
 from css_parser import css as cp_css
 
 from ebook_converter import constants as const
-from ebook_converter import guess_type
 from ebook_converter.ebooks import unit_convert
 from ebook_converter.ebooks.oeb import base
 from ebook_converter.ebooks.oeb import parse_utils
@@ -125,8 +125,9 @@ class EmbedFontsCSSRules(object):
             rules = [base.css_text(x) for x in self.rules]
             rules = '\n\n'.join(rules)
             sheet = css_parser.parseString(rules, validate=False)
-            self.href = oeb.manifest.add(iid, href, guess_type(href)[0],
-                    data=sheet).href
+            self.href = oeb.manifest.add(iid, href,
+                                         mimetypes.guess_type(href)[0],
+                                         data=sheet).href
         return self.href
 
 
@@ -244,7 +245,7 @@ class CSSFlattener(object):
             fid, href = self.oeb.manifest.generate(id=u'font',
                 href='fonts/%s.%s'%(ascii_filename(font['full_name']).replace(' ', '-'), ext))
             item = self.oeb.manifest.add(fid, href,
-                    guess_type('dummy.'+ext)[0],
+                    mimetypes.guess_type('dummy.'+ext)[0],
                     data=font_scanner.get_font_data(font))
             item.unload_data_from_memory()