Also adds Sentinel to appveyor, we hope. Or this will fail miserably.

These get overwritten when run, so they're ignored via:
git update-index --assume-unchanged RedisConfigs\Sentinel\sentinel-26379.conf

To make changes that should propagate to others:
git update-index --no-assume-unchanged RedisConfigs\Sentinel\sentinel-26379.conf

If we're AddressFamily.Unspecified, that'll always error. Assume IPv4 (as we did before).

This fixes connecting to IPv6 servers.

This adds IPv4 parsing and connect testing, verified that the fix in #686 will work.

Before converting most of the project to C# 7, `netstandard2.0`, etc. I want to get unit tests in shape. There's a fair bit of complication to doing so in that we need to test against:
- Different versions
- Clusters
- Master/Slave setups
- Multiple-test unfriendly tests (like SHUTDOWN commands)
- Simulate remote (read: latent) connections

This work does a few things:
- Moves all unit tests and assertions to xUnit
- Enables parallelization for tests
- Utilizes the xUnit output semantics, which means things like connection logs are on the test in VS, console output, build servers, etc. (it was a giant pool of `Console.WriteLine` mixed before)
- Cleans up the `\packages` folder completely (it wasn't used for anything but the `redis-*.exe` binaries
- Cleans up all test code formatting in general
- Re-enables `net462` in testing (was only `netcoreapp1.0` before)
- Allows overrides via `TestConfig.json`
- Updates all the RedisConfig\ scripts for easy test running
- Adds a StackExchange.Redis.Tests\README.md
- Fixes many tests

Remaining Long-term TODOs
- Look at Redis 4.0 on Windows via WSL
- Configure endpoints in a `.json` config override that's in `.gitignore`
- Find a way to handle master/slave breaks on underpowered machines better

Fixed the URL to the properties of <processModel in machine.web, added a comment regarding using the value in web.config (it's not possible)

Issue 690 - Fixed the return of methods GetItemsAsGeoPosition and GetItemsAsGeoPositionArray on RawResult.cs, now these methods respect the constructor of GeoPosition obj.

fix markdown link syntax in doc

Oh... my... looks like FEATURE_SOCKET_MODE_POLL hasn't been defined for... a while! This is very bad

Feature- NRediSearch Sorting Functionality

Fix pack re https://github.com/NuGet/Home/issues/4853 (note build.cmd as slightly awkward to invoke)

NRediSearch; prepare for deploy