Improvements in the function expand_root_word_for_ngram()

[dimztimz]

This function now behaves same as in Hunspell bit it can be improved to allow certain combinations of prefix and suffix related to the flags CIRCUMFIX and NEEDAFFIX.

The second improvement is getting better performance by adding some indexing over the stripping affixes, or over the flag of the affixes. This will speed up the searching of matching affix entries. This improvement requires changes in the data structures, thus changing ABI, which requires bump of the major version.