Crappy characters ordering issue

Fix accent conversion issue.

Problem: '{\\"u} \\"{u}'}' wouldn't convert toa 'ü ü'.

Reason: The conversion starts from \\" instead of {\\"u}.

Solution:
    * Make unicode_to_*latex as an ordered tuple.
    * Remove duplicate mapping in unicode_to_crappy_latex1.
    * Add a test for '{\\"u} \\"{u}'}'.
    * (Minor) Use itertools.chain() to simplify code.
    * (Minor) Update README to mention Python 2.7.