framework and tooling lib updates; does *NOT* include the full corpus of 3rd party ADO.NET providers

This is a branch cleaning up old `#if` clauses, `.csproj` bits, Linux build compatibility, and a few other tid-bits (broken out by commit).

In general: we're on 3.0 tooling and all previous cruft has been removed.

…cording to their names.

Hand coded version did not operate under the same circumstances as others.

- Add CommandBehavior.SingleResult and CommandBehavior.SingleRow. All other framworks does this under the hood.
- Run SqlCommand.Prepare() (perhaps it should be benchmarked as "Compiled"?)
- Use GetNullableValue because it's easier to read and slightly faster
- _table.Rows was incrementally added, which made the benchmark run slower the longer it executed. Added _table.Rows.Clear() to prevent the growth.
- Changed select to use * like other benchmarks

Hi!
This PR tries to fix Dapper.Performance.Tests, actually you can't get [MemoryDiagnoser](https://benchmarkdotnet.org/api/BenchmarkDotNet.Diagnosers.MemoryDiagnoser.html)  stats because 
```IDiagnoser.GetColumnProvider()``` method was gone on BenchmarkDotnet 0.11.2. I choose ```DefaultColumnProviders.Metrics``` because of [this](https://github.com/dotnet/BenchmarkDotNet/issues/1184#issuecomment-507377695), i think it's the most simple way to add stats now.

**Before**
![image](https://user-images.githubusercontent.com/34173061/65264060-1a5f7780-db0e-11e9-9c8c-bb4c69a808df.png)

**After**
![image](https://user-images.githubusercontent.com/34173061/65264158-4f6bca00-db0e-11e9-9313-597b09070ae6.png)

On the other hand i choose removing ```[Ordered]``` as temporal solution of https://github.com/dotnet/BenchmarkDotNet/issues/1238, and yeah, the results are still ordered because of https://github.com/StackExchange/Dapper/blob/9282ef2872e1c82c68c86f31e93e8f1ceaacd409/Dapper.Tests.Performance/Config.cs#L42

**Before**
![image](https://user-images.githubusercontent.com/34173061/65264660-6232ce80-db0f-11e9-9046-9c2d8fc5e2d8.png)

**After**
 (No errors)

Thanks for all!!

Fix issue #418 for DeleteAsync (with tests)

* Handle char correctly

* Add PostgreSQL char test

* Test for string before testing for char

v2 work; primarily prep for split SqlClient

Expose the underlying connection from Rainbow Database so it's easier to use Dapper alongside other DB frameworks (#1257)

* Pass LocalBuilders instead of indexes since ILGenerator already optimizes the opcode used

* Eradicate magic local indexes to make refactoring safer

* String and byte[] tuple elements cause InvalidProgramException

* Stop setting current index local which is nonexistent in ValueTuple deserializer

* prep work for adding Microsoft.Data.SqlClient support/tests; SqlClient dependency is not yet removed

* Failing tests for tuples larger than 7

* Special-case IL generation for ValueTuple

* Make value-processing logic available to ValueTuple generation

* fix #1228 - rev sqlclient to 4.6.0
* use transitive deps for SqlClient