Use the real constants module.

This is progressing refactor of the calibre code to make it more
readable, and transform it to something more coherent.

In this patch, there are changes regarding imports for some modules,
instead of polluting namespace of each module with some other modules
symbols, which often were imported from other modules. Yuck.

ebook_converter/ebooks/oeb/transforms/manglecase.py

@@ -5,9 +5,9 @@ import string
 
 from lxml import etree
 
-from ebook_converter.ebooks.oeb.base import XHTML, XHTML_NS
-from ebook_converter.ebooks.oeb.base import CSS_MIME
-from ebook_converter.ebooks.oeb.base import namespace
+from ebook_converter import constants as const
+from ebook_converter.ebooks.oeb import base
+from ebook_converter.ebooks.oeb import parse_utils
 from ebook_converter.ebooks.oeb.stylizer import Stylizer
 
 
@@ -43,15 +43,16 @@ class CaseMangler(object):
 
     def mangle_spine(self):
         id, href = self.oeb.manifest.generate('manglecase', 'manglecase.css')
-        self.oeb.manifest.add(id, href, CSS_MIME, data=CASE_MANGLER_CSS)
+        self.oeb.manifest.add(id, href, base.CSS_MIME, data=CASE_MANGLER_CSS)
         for item in self.oeb.spine:
             html = item.data
             relhref = item.relhref(href)
-            etree.SubElement(html.find(XHTML('head')), XHTML('link'),
-                             rel='stylesheet', href=relhref, type=CSS_MIME)
+            etree.SubElement(html.find(base.tag('xhtml', 'head')),
+                             base.tag('xhtml', 'link'), rel='stylesheet',
+                             href=relhref, type=base.CSS_MIME)
             stylizer = Stylizer(html, item.href, self.oeb, self.opts,
                                 self.profile)
-            self.mangle_elem(html.find(XHTML('body')), stylizer)
+            self.mangle_elem(html.find(base.tag('xhtml', 'body')), stylizer)
 
     def text_transform(self, transform, text):
         if transform == 'capitalize':
@@ -85,7 +86,8 @@ class CaseMangler(object):
                 else:
                     last.tail = text
             else:
-                child = elem.makeelement(XHTML('span'), attrib=attrib)
+                child = elem.makeelement(base.tag('xhtml', 'span'),
+                                         attrib=attrib)
                 child.text = text.upper()
                 if last is None:
                     elem.insert(0, child)
@@ -99,7 +101,7 @@ class CaseMangler(object):
 
     def mangle_elem(self, elem, stylizer):
         if not isinstance(elem.tag, (str, bytes)) or \
-           namespace(elem.tag) != XHTML_NS:
+           parse_utils.namespace(elem.tag) != const.XHTML_NS:
             return
         children = list(elem)
         style = stylizer.style(elem)