Fix DebuggerDisplay for GraphQLFragmentDefinition (graphql-dotnet#249)

Add support for description parsing (graphql-dotnet#132)

Add support for '&' syntax token (graphql-dotnet#126)

Merge branch 'master' of github.com:graphql-dotnet/parser into develop

# Conflicts:
#	src/GraphQLParser.Tests/GraphQLParser.Tests.csproj

Remove setters from ISource/Source (graphql-dotnet#97)