Drop single drop-in file and T4 templates(?)

[tmenier]

From the start, PetaPoco was available to use as a single drop-in C# file, an idea most likely inspired by Dapper. Today, NuGet is so ubiquitous that I think it's time to part ways with this approach. (Dapper dropped theirs several years ago in version 1.50, for the same reason.) Among other things, it'll allow the removal of the entire "csj" project, a console app that gets run on post-build of the main project and whose job it is to join a number of cs files into the single AsyncPoco.cs file.

The T4 templates I'm a little less certain about, but I suspect they're less useful these days too. They were largely inspired by Rob Conery's Subsonic project, which has pretty much been dead since .NET 3.5, and I don't think most modern ORMs include this feature. On one hand it doesn't hurt to keep them, but on the other hand they've gone untested and unmaintained for years, and I'm not sure I want to commit to maintaining them going forward if no one's using them.

Note that these features will always be available in 1.x, but as of now I don't plan on bringing the over to 2.x, which (for starters) is all about .NET Core support.

Please chime in if you have any opinions on this one way or the other.