* Don't create the connection in Dispose: this avoids creating a SQLConnection simply to Dispose it.
* Run MySQL tests against the open MySqlConnection: 'connection' is a protected variable in the TestBase class that is a SQL Server connection, not a MySQL connection.
* Skip broken MySQL tests: as per issue #295, setting "AllowZeroDateTime=True" in the connection string causes an InvalidCastException in SqlMapper.

This adds a netstandard2.0 build to Dapper (and StrongName until v2),
adds a netstandard2.0 test lineup, restores most functionality (except
UDTs for SQL, e.g. .UdtTypeName isn't in netstandard2), and also breaks
things not actually implemented or implemented correctly in
netstandard2.0. Pushing this up so we can work through these with the
.NET teams.

Several things are still broken here (and fail tests):
- Parameter decimal values (not filed yet)
- DataTables as parameters
(https://github.com/dotnet/corefx/issues/19708)
- .GetSchemaTable() (not yet filed, implementation is completely missing
from SqlDataReader in CoreFX)

While the compile is clean, the above are runtime issues.
`SqlParameter.UdtTypeName` is a separate issue, that one just wasn't in
`netstandard2.0` at all...so we can't support UDTs there until it is.
See https://github.com/dotnet/corefx/issues/17126 for details.

More cleanup to do (removing Type column next), but getting to some very
usable output now.

This is based on BenchmarkDotNet (while preserving the legacy format
with minor improvements as well - legacy runs much faster). See #666 for
details. Not an ominus number at all.

Note: this code will get a bit simpler with BenchmarkDotNet categories,
see https://github.com/dotnet/BenchmarkDotNet/issues/248 for details.

It's indeed broken on their end. We should consider switching providers,
e.g. https://github.com/mysql-net/MySqlConnector/

* Progress on VS 2017 build tooling
* Finally, a working VS 2017 tooling build

Add tests for the too few/too many columns scenarios for value-tuples; happy to discuss alternative expectations

Better matching of value-tuple names when wrong number of columns - should return nulls for unmapped