Add all the missing First/Single/SingleOrDefault methods to match the FirstOrDefault added previously

Fix for #281 - Change CommandBehavior on ExecuteReaderAsync to match sync version

Just removing some overhead here

Remove some unused casts, variables, and warnings

Use single-row/single-result hint when possible

MySQL Test Suite for Contrib

Fix the URL to the Tests file in Readme

Fix the url to Dapper Tests

This is the "approved" xUnit pattern, via:
https://github.com/xunit/samples.xunit/tree/master/DynamicSkipExample
It's also the only way I can make the damn skipping work...but at least
it's it's one-time code to make any server set relatively easily
skippable.

Add {Query|Read}FirstOrDefault methods with optimized paths

Fix all `(object)param` and `dynamic param` declarations; we already fixed this for non-async, but it looks like it was missed for async; this is not a breaking change: `dynamic` is actually `object`+attribute

Add {Query|Read}FirstOrDefault methods with optimized paths; remove redundant `return await` constructs (prefer to return the existing Task)

Make DefaultTypeMap public again

TODO: Figure out a clean way to disable this locally - we'll want this
functionality in the Core test suite as well as we add MySQL specific
tests (due to syntax differences in creating tables and such).

This fixes some MySQL issues - test suite that confirms issues and fixes
is incoming. TODO shortly after: implement the Insert<T, TKey> style
methods. I just want to get tests running (and some added) first.