Avoid Python 2 ur'string' syntax

Continue to use u'unicode' strings as elsewhere in conf.py, but these
literals use no backslash escapes anyway so there's no need for r'raw'.
Fixes #1019.

doc/conf.py

@@ -201,8 +201,8 @@
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title, author, documentclass [howto/manual]).
 latex_documents = [
-    ('index', 'pysam.tex', ur'pysam documentation',
-     ur'Andreas Heger, Kevin Jacobs et al.', 'manual'),
+    ('index', 'pysam.tex', u'pysam documentation',
+     u'Andreas Heger, Kevin Jacobs, et al.', 'manual'),
 ]
 
 # The name of an image file (relative to this directory) to place at the top of