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

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.

Assuming the CHSARP30 were oversights here given the net35 removal, but
playing it safe and leaving for this commit.

Provided a name for MySql LAST_INSERT_ID call to allow the result to …

A full CoreCLR/DNX friendly conversion

Updated link to performance tests.

This eliminates the dual solutions and brings Contrib into the
project.json fold.
- Tests are ported to xUnit though SQLite is disabled on DNX due to
Issue #375 (Interop loads fail in the VS runner and  params are busted
regardless).
- Projects are consolidated down to what's currently possible with
project.json.
- Contrib moved to: Dapper.Contrib and Dapper.Tests.Contrib (so tests
appear at the end, no other reason vs. Dapper.Contrib.Tests)
- EF moved to: Dapper.EntityFramework(.StrongName)
- Rainbow moved to: Dapper.Rainbow
- SqlBuilder moved to: Dapper.SqlBuilder
- Packages are removed since it's not current-tooling friendly to keep
them (nor was it using them).
- xUnit implemented in Contrib via abstracts - this allow us to very
quickly add any database provider to the rig in a very concise way.
- Contrib unit tests fixed in various places - they were not
parallel-runner friendly
- Nuspecs removed, since they aren't used anymore (to eliminate
confusion)
- Removed speed tests for libraries that aren't on current versions of
.Net (what would we be comparing?)
- Perf tests moved to Dapper.Tests (consolidation from
Dapper.DNX.Tests), but aren't activated yet (no define)

Fixed missing check for explicit key in Contrib GetaAync()

hacky style - I think we want to remove the program given dnx run exists

This allows full testing from both solutions, all green.

This includes nuget updates for the test libraries but explicitly
excludes the npgsql upgrade, since there are known 2.0 vs. 3.0 driver
issues. If we can assume everyone is able to upgrade - then we should
switch testing over. Alternatively, we need to test both. My preference
would be the former.

This reverts commit 4a70b621.