Add morphological constructs

[Sintrastes]

See here for some different types of morphology. We'll probably start by some simple examples (such as suffixes) in English, and go on to add other examples.

This presents some interesting computational challenges, as we will need to find a way of translating from raw words to their morphological interpretations. Perhaps (at least for suffixes) a trie-like data structure might be useful for this purpose.