* Build Update
- Change `TargetFramework` to `netcoreapp2.1` and removed unnecessary `RuntimeFrameworkVersion` from `PowerShell.Common.props`
- Update dotnet SDK to 2.1.300-rc1-008662
- Update `TypeGen` target in `Build.psm1` to work with 2.1
- Rename macOS runtime to `osx-x64` as the old build logic expects 10.12 and breaks running on 10.13 system.
- Remove `PackageReference` to `System.Memory` as it's part of dotnetcore 2.1
- Update search for `crossgen` executable to find the matching version
* Test Update
- Update test tools `WebListener` to latest `asp.net core`
- Marked `AuthHeader Redirect` tests as `Pending` due to change in CoreFX
* Rebase onto .NET Core 1.1
Modify `Build.psm1` and `project.json` files to use .NET Core 1.1.
.NET Core 1.1 ships with an older dotnet/cli than has currently been used,
so we revert to use case-sensitive directory names for dependencies.
.NET Core 1.1 is a pre-requisite for supporting Fedora 24.
* PSReadLine: Bump major version of PSReadline to 6.0.0-*
* Microsoft.PowerShell.Commands.Utility: Bump major version of Microsoft.CodeAnalysis.Csharp
* Microsoft.PowerShell.SDK: Revert attempt to import netcoreapp1.1 instead of dnxcore
* build.psm1: Restore ability to specify version of dotnet-install.sh
