Feature Request: add MSSQL support

[joshgav]

Add Azure MSSQL Database to Buffalo database types, by adding MSSQL support to pop.

Looks like we'd need to add an mssql dialect [1] similar to the mysql [2] and postgres [3] ones.

Some work has begun in https://github.com/gobuffalo/pop/issues/40.

Docs on connecting to MSSQL in Go: https://docs.microsoft.com/en-us/azure/sql-database/sql-database-connect-query-go.