Fixup NuGet.Config and project.json to get things to compile; core-clr: the gift that keeps on giving

Code cleanup - take 2

- Expression bodies
- Auto-properties (also get-only properties)
- Null propagation
- `nameof` operator
- String interpolation
- Dictionary initializer
- await in finally clause

Add `System.Xml` framework assembly

Without it, Resharper complains about needing the `System.Xml` module when using the `DataTable` class. Project compiles fine without it though. The .NET 4 .csproj file included it as well.

fixed GetAll when used with ExplicitKey

Merge branch 'projectlock' of https://github.com/sebastienros/dapper-dot-net into sebastienros-projectlock

Conflicts:
	Dapper.DNX.Tests/project.lock.json
	Dapper/project.lock.json

DNX improvements

Added global.json to solution items too.

These files are already ignored but must have been added before the rule was added.

The "SqlMapper.cs is too damned big" file split; also removes C#3 support and .NET 3.5 support (sorry, but legacy by too many years)

Fix broken link in README

Fixes #357