c2/20 made conversion table
c2/21 added new test 'ignores non alphabetics' and made test pass
c2/22 add new test 'replaces multiple consonants with digits'
c2/23 disable a test and refactor encode
c2/24 enable the test, extend encodedDigits to encode multiple chars.
c2/25 remove guard clause which is no more needed
c2/26 add new test 'limits length to four characters'
c2/26 encodedDigits encodes MAX_CODE_LENGTH length
c2/27 extract method isComplete from encodedDigits
c2/28 add new test 'ignores vowel like letters' and it passes
c2/29 add new test 'combines duplicate encodings'