Updated .csproj package version and release notes for 0.6.1

Updated .csproj package version and release notes for 0.6.0

- Also added changes.txt.

Added IDictionary<string, VToken> as a superclass of VObject

- Also fixed namespaces from the previous commit.

Fixed SOE on deserializing an empty input

- Added VdfException type to allow handling invalid input.
- Fixes shravan2x#5.

Added extensions list to README

Merge branch 'master' of https://github.com/Shravan2x/Gameloop.Vdf

Fixed strings not being escaped during serialization

Retargeted project to .NET Standard 1.0

- Removed unused code and interfaces.

Added dynamic property binding for VObject

- Borrowed a few MIT licensed utils from Json.Net.

Updated README for NuGet

Directed user to NuGet or releases page to get binaries.