Analyzers with parameters

[osma]

Currently we have three analyzers (fi, sv, en) all based on NLTK SnowballStemmer. This leads to duplicated code. Adding more languages would imply adding more analyzers.

We could instead have just one SnowballAnalyzer that takes a language parameter. Then it could be configured like this:

analyzer=snowball(finnish)

or why not

analyzer=snowball(french)

A similar approach would work for libvoikko (#37) which supports several languages:

analyzer=voikko(fi)

The parameter would be passed directly to the algorithm so all languages supported by the stemmers/lemmatizers would be available.