Convert calibre modules to ebook_converter.

Here is the first batch of modules, which are needed for converting
several formats to LRF. Some of the logic has been change, more cleanups
will follow.

ebook_converter/utils/html2text.py

@@ -8,7 +8,7 @@ def html2text(html):
     from html2text import HTML2Text
     import re
     if isinstance(html, bytes):
-        from calibre.ebooks.chardet import xml_to_unicode
+        from ebook_converter.ebooks.chardet import xml_to_unicode
         html = xml_to_unicode(html, strip_encoding_pats=True, resolve_entities=True)[0]
     # replace <u> tags with <span> as <u> becomes emphasis in html2text
     html = re.sub(