Move C# 7.1 proposals to 7.1 folder (#870)

Author: jcouv

.gitignore

@@ -0,0 +1,5 @@
+
+# Ignore temporary files
+~$*
+*~
+

proposals/csharp-7.1/README.md

@@ -1,7 +1,8 @@
 
 # C# 7.1
 
-- [Async Main](https://github.com/dotnet/csharplang/blob/master/proposals/async-main.md) 
-- [Default Expressions](https://github.com/dotnet/csharplang/blob/master/proposals/target-typed-default.md) 
+- [Async Main](https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.1/async-main.md)
+- [Default Expressions](https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.1/target-typed-default.md)
 - [Infer tuple names](https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.1/infer-tuple-names.md)
-- [Pattern-matching with generics](https://github.com/dotnet/csharplang/blob/master/proposals/generics-pattern-match.md) 
+- [Pattern-matching with generics](https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.1/generics-pattern-match.md)
+