Permit to set a maximum page_size

Fixes #70 and adds the first and last page hrefs
I needed it in order to pass some parameters to do custom filters and for those the can_filter_by wasn't enough.

For example, to pass a params[:max_price] = 50.0 in order to limit the scope to a price < 50.0, or on an enum (mapped on the db as integers) passing params[:status] = 'shipped', and having the scope as status = enum['shipped'], or even with multiple values (status in (enum['shipped'], enum['delivered'])).

Adding :max_price and :status as custom parameters (or a better name if we can find it :) ) permits to have them returned in the page urls, filtering out all those not allowed.