Update get_letters to be fast.
Update get_letters to be fast.

        1    0.002    0.002    0.037    0.037 utf8.py:11(<module>)
        1    0.000    0.000    0.000    0.000 utf8.py:160(<listcomp>)
      288    0.001    0.000    0.001    0.000 utf8.py:235(uyir_len)
      288    0.001    0.000    0.001    0.000 utf8.py:238(mei_len)
      288    0.004    0.000    0.006    0.000 utf8.py:275(uyirmei_constructed)
    98518    1.310    0.000    2.257    0.000 utf8.py:304(<lambda>)
        4    0.000    0.000    0.000    0.000 utf8.py:385(_make_set)
    64097    5.427    0.000   10.088    0.000 utf8.py:394(get_letters)
        1    0.000    0.000    0.000    0.000 utf8.py:760(CacheGetLettersMixin)
        1    0.000    0.000    0.000    0.000 utf8.py:762(__init__)
    64118    1.538    0.000   13.998    0.000 utf8.py:769(get_letters)
        1    0.000    0.000    0.000    0.000 wordutils.py:313(DictionaryFixedWordList)
        1    0.000    0.000    0.033    0.033 wordutils.py:4(<module>)
>>>>>>>>>. after optimization .<<<<<<<<<<<<<
        1    0.002    0.002    0.035    0.035 utf8.py:11(<module>)
        1    0.000    0.000    0.000    0.000 utf8.py:160(<listcomp>)
      288    0.001    0.000    0.001    0.000 utf8.py:235(uyir_len)
      288    0.001    0.000    0.001    0.000 utf8.py:238(mei_len)
      288    0.003    0.000    0.005    0.000 utf8.py:275(uyirmei_constructed)
    98518    0.824    0.000    1.219    0.000 utf8.py:303(is_tamil_unicode_predicate)
        4    0.000    0.000    0.000    0.000 utf8.py:387(_make_set)
    64097    4.438    0.000    7.756    0.000 utf8.py:396(get_letters)
        1    0.000    0.000    0.000    0.000 utf8.py:762(CacheGetLettersMixin)
        1    0.000    0.000    0.000    0.000 utf8.py:764(__init__)
    64118    1.296    0.000   11.101    0.000 utf8.py:771(get_letters)
        1    0.000    0.000    0.000    0.000 wordutils.py:313(DictionaryFixedWordList)
        1    0.000    0.000    0.033    0.033 wordutils.py:4(<module>)
>>>>>>>>>> final optimization <<<<<<<<<<<<<<
      1    0.002    0.002    0.033    0.033 utf8.py:11(<module>)
        1    0.000    0.000    0.000    0.000 utf8.py:1415(CacheGetLettersMixin)
        1    0.000    0.000    0.000    0.000 utf8.py:1418(__init__)
    64118    0.552    0.000    7.253    0.000 utf8.py:1425(get_letters)
        1    0.000    0.000    0.000    0.000 utf8.py:398(<listcomp>)
      288    0.001    0.000    0.001    0.000 utf8.py:778(uyir_len)
      288    0.001    0.000    0.001    0.000 utf8.py:782(mei_len)
      288    0.005    0.000    0.007    0.000 utf8.py:828(uyirmei_constructed)
    98560    0.385    0.000    0.385    0.000 utf8.py:860(is_tamil_unicode_value)
        4    0.000    0.000    0.000    0.000 utf8.py:965(_make_set)
        1    0.000    0.000    0.000    0.000 utf8.py:982(copy_lru_decorator)
    64118    0.713    0.000    7.966    0.000 utf8.py:983(f_lru)
    64118    1.216    0.000   10.279    0.000 utf8.py:987(f_copy_lru)
    64118    3.805    0.000    6.047    0.000 utf8.py:995(get_letters)
=========================================================================

Ezhil-Language-Foundation/open-tamil,Ezhil-Language-Foundation/open-tamil,Ezhil-Language-Foundation/open-tamil,Ezhil-Language-Foundation/open-tamil,arcturusannamalai/open-tamil,arcturusannamalai/open-tamil,arcturusannamalai/open-tamil,arcturusannamalai/open-tamil,Ezhil-Language-Foundation/open-tamil,arcturusannamalai/open-tamil,Ezhil-Language-Foundation/open-tamil,Ezhil-Language-Foundation/open-tamil,Ezhil-Language-Foundation/open-tamil,arcturusannamalai/open-tamil,arcturusannamalai/open-tamil,Ezhil-Language-Foundation/open-tamil