renamed validate_letter to assert_valid_letter and rewrote it in
accordance with PEP8 and Python style guidelines
Made get_aytham() PEP8 and Python Style Guide-compliant
Made get_vowels() PEP8 and Google Style guide-compliant
Rewrote get_vowels() and get_consonants() for efficiency. Rewrote
get_consonants() to conform with PEP8 and Google Style guidelines
TamilLetter.validate_letter() renamed to assert_valid_letter()
Merge pull request #5 from abmohan/master

Improvements to TamilLetter, and PEP8 and Google Python Style guide conformance changes