Tag Mapper: Allow Title-casing of tags. Fixes #1823097 [Feature Request: Tag Mapper Option - Title Case](https://bugs.launchpad.net/calibre/+bug/1823097)

src/calibre/ebooks/metadata/tag_mapper.py

@@ -82,6 +82,10 @@ def apply_rules(tag, rules):
                 if ac == 'capitalize':
                     ans.append(tag.capitalize())
                     break
+                if ac == 'titlecase':
+                    from calibre.utils.titlecase import titlecase
+                    ans.append(titlecase(tag))
+                    break
                 if ac == 'lower':
                     ans.append(icu_lower(tag))
                     break
@@ -149,6 +153,7 @@ def find_tests():
                 self.assertEqual(ans, expected)
 
             run(rule('capitalize', 't1,t2'), 't1,x1', 'T1,x1')
+            run(rule('titlecase', 'some tag'), 'some tag,x1', 'Some Tag,x1')
             run(rule('upper', 'ta,t2'), 'ta,x1', 'TA,x1')
             run(rule('lower', 'ta,x1'), 'TA,X1', 'ta,x1')
             run(rule('replace', 't1', 't2'), 't1,x1', 't2,x1')

src/calibre/gui2/tag_mapper.py

@@ -47,6 +47,7 @@ class RuleEdit(QWidget):
                 ('replace', _('Replace')),
                 ('keep', _('Keep')),
                 ('capitalize', _('Capitalize')),
+                ('titlecase', _('Title-case')),
                 ('lower', _('Lower-case')),
                 ('upper', _('Upper-case')),
                 ('split', _('Split')),

src/calibre/utils/titlecase.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python2
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 """
 Original Perl version by: John Gruber https://daringfireball.net/ 10 May 2008