AnalyzingSuggester pretends it can handle contexts

I'm perhaps (ironically?) missing some context here but -

I find it weird that AnalyzingSuggester does not support contexts 
but has a `lookup` method arity that accepts a `contexts` argument 
(!). If you call it with anyting but null there it throws, but 
still seems odd.

In addition, it also does not document that it does not support 
contexts. The user will typically find out about this when they 
supply an InputIterator to `build` with contexts, and it throws.

(I have sent a few messages likes this noting documentation 
omissions; if pull requests or patches are welcomed please let me 
know.)