Pass 'IgnoreNonAlphabet' tests

Test condition not presents in specification; it added by customer or
googling.
Refactoring: encode tail of the word
Replacing multiple consonants with loop
Refactoring: remove unused guard condition
Limit encoding length to 4 characters
Add test to ignore vowel-like characters

Test passes, what is bad. Test demonstrates what happens for any
unrecognized chars. We need to create another test.