Feature/mssql dialect

I was going to split this up into just the tests and then just the dialect files, but we'd lose history that way and it's still manageable this way. Of course let me know if you have any questions. Questions I have for YOU guys should be noted in the code (specifically with "NOTE" comments, of particular interest is the datatypes BLOB field tests).

I don't imagine this is getting in right away at all, but I've been pretty diligent about it and currently all tests pass with flying colors. Still left to be done: proper schema support, replacing all identifier quoting with brackets instead of quotes, transaction support.

Not sure how to "add" people to this, but hopefully this does it: @sdepold @mickhansen @janmeier @thecaddy 

This doesn't necessarily need to be `EXISTS` if there's any type of method that is supported by all dialects.