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/conversion/plugins/fb2_input.py

@@ -1,6 +1,7 @@
 """
 Convert .fb2 files to .lrf
 """
+import mimetypes
 import os
 import pkg_resources
 import re
@@ -10,7 +11,6 @@ from lxml import etree
 from ebook_converter import constants as const
 from ebook_converter.customize.conversion import InputFormatPlugin
 from ebook_converter.customize.conversion import OptionRecommendation
-from ebook_converter import guess_type
 
 
 FB2NS = 'http://www.gribuser.ru/xml/fictionbook/2.0'
@@ -152,7 +152,8 @@ class FB2Input(InputFormatPlugin):
                     break
 
         opf = OPFCreator(os.getcwd(), mi)
-        entries = [(f2, guess_type(f2)[0]) for f2 in os.listdir(u'.')]
+        entries = [(f2, mimetypes.guess_type(f2)[0])
+                   for f2 in os.listdir(u'.')]
         opf.create_manifest(entries)
         opf.create_spine(['index.xhtml'])
         if cpath: