First PR for Npgsql technical debt cleanup

I've started with the codebase cleanup. As a lot of the code is a bit chaotic due to all the changes done over the past years by various authors, it's best to clean the stuff up a bit, weed out dead code and the like, restructure files, make everything look the same and professional and more predictable, so it's easier to understand when reading the code. 

I've started with the connectionstring builder. I had cleaned up the connection class as well, but that was in v2.2, and as it changed a lot in v3 branch, I'll re-do that one later. 

(all tests pass)
Yeah, it's a codebase with a lot of history and a lot of different contributors (I only started working on Npgsql pretty recently). It's not that big a deal though, I do styling commits every now and then.

Your rules look great, we should copy a lot of it. For some things I like to do it a bit differently, we don't necessarily have to make decisions on everything:
* I think regions are really helpful to group together methods in a class that belong together (see NpgsqlConnector). Sometimes I even include members, properties, events and delegates in these "thematic" regions.
* Like I said I almost never use "this" in general, adds a bit too much text for my taste...