Add some small features missing from the tracker.

Author: Neal Gafter

admin/v7-feature-tracker.md

@@ -31,7 +31,8 @@ Version | Feature | PR | Status | Effort | Notes
 7.2 | Conditional `ref` expressions ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.2/conditional-ref.md)) | [213](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/213) **but needs work**  | Open | Medium | Feature Group E.
 7.2 | `in` parameter modifier ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.2/readonly-ref.md)) | [219](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/219) | Open | Medium | Feature Group F.
 7.2 | `ref` with `this` in extension methods ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.2/ref-extension-methods.md)) | [219](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/219) | Open | Medium | Feature Group F.
-7.2 | `readonly` and `ref` structs ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.2/readonly-struct.md)) | [333](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/333) | Open | Small | 
+7.2 | `readonly` structs ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.2/readonly-struct.md)) | [333](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/333) | Open | Small | 
+7.2 | `ref` structs ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.2/span-safety.md)) | [333](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/333) | Open | Medium | 
 7.3 | indexing movable fixed buffer without pinning ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.3/indexing-movable-fixed-fields.md)) | [239](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/239) | Open | Small |  
 7.3 | reassign `ref` local variables ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.3/ref-local-reassignment.md)) | [213](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/213) **but needs work**  | Open | Medium | Feature Group E.
 7.3 | use initializers on `stackalloc` arrays ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.3/stackalloc-array-initializers.md)) | [238](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/238) | Open | Small | 
@@ -41,3 +42,6 @@ Version | Feature | PR | Status | Effort | Notes
 7.3 | use expression variables in more locations ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.3/expression-variables-in-initializers.md)) | [44](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/44), [61](https://github.com/ECMA-TC49-TG2/csharpstandard/pull/61) | Open | Medium | Feature Group B and D.
 7.3 | attach attributes to the backing field of auto-implemented properties ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.3/auto-prop-field-attrs.md)) | [262](https://github.com/dotnet/csharpstandard/pull/262) | Open | Small | 
 7.3 | overload resolution now has fewer ambiguous cases ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-7.3/improved-overload-candidates.md)) | [263](https://github.com/dotnet/csharpstandard/pull/263) | Open | Small | 
+7.3 | this ref vs ref this ([MS Proposal](https://github.com/dotnet/csharplang/blob/main/meetings/2017/LDM-2017-12-04.md#this-ref-vs-ref-this)) | | | | Small |
+7.3 | by value vs in overload tiebreaker ([MS Proposal](https://github.com/dotnet/csharplang/issues/945)) | | | | Small |
+7.3 | permit `System.Enum` and `System.Delegate` as constraints ([MS proposal 1](https://github.com/dotnet/csharplang/issues/104) [MS proposal 2](https://github.com/dotnet/csharplang/issues/103)) | | | | Small |