Added 5 new Tamil encodes in txt2unicode module

Update txt2unicode with 5 new Tamil encodes Diacritic, Shreelipi, Softview, Tace & Vanavil.
Also updated .travis.yml to install package only for python 2.6 version
Enabled 2.6 python unitttest for txt2unicode all 5 unittest.
Updated 3 Readme files with new 5 encodes.