[doc] Describe available client options.

It took me a while to find a decent and concise form to describe each client option since they are inherently more complex than connection parameters due to the multitude of different values they accept, but I think (hope?) I finally reached an acceptable result.

Since most client options are strictly related to macro-arguments that will be covered through the rest of the documentation (e.g. clustering, replication, etc), I placed various cross references to other documents. Each specific document should include a section about its corresponding client option  with a more extensive description focusing on some configuration scenarios or possible side effects.

Thoughts?