Change "better conversion target" to not require an expression

This effectively moves the method group aspect up from 11.6.4.6 to
11.6.4.4.

Notes:

I've added "for conversion C1" to the "single best method from the
method group" part as the single best method may be different for C1
and C2 - there's no single best method from a method group without
a specific method group conversion being considered

The rule doesn't refer to T2/C2, but I don't think it has to...
because it's valid for both conversions to be better than the other.
That's already the case in better conversion target, as types T1 and
T2 could both have implicit conversions to each other.

I think this means we could also remove "and E does not exactly
match T2" in the first rule of 11.6.4.4, but I haven't gone that far
in this PR.

Fixes #549
Fixes #550

Author: jskeet

standard/expressions.md

@@ -1000,10 +1000,11 @@ In case the parameter type sequences `{P₁, P₂, ..., Pᵥ}` and `{Q₁, Q₂
 
 #### 11.6.4.4 Better conversion from expression
 
-Given an implicit conversion `C₁` that converts from an expression `E` to a type `T₁`, and an implicit conversion `C₂` that converts from an expression `E` to a type `T₂`, `C₁` is a better conversion than `C₂` if one of the following holds:
+Given an implicit conversion `C₁` that converts from an expression `E` to a type `T₁`, and an implicit conversion `C₂` that converts from an expression `E` to a type `T₂`, `C₁` is a ***better conversion*** than `C₂` if one of the following holds:
 
 - `E` exactly matches `T₁` and `E` does not exactly match `T₂` ([§11.6.4.5](expressions.md#11645-exactly-matching-expression))
 - `E` exactly matches both or neither of `T₁` and `T₂`, and `T₁` is a better conversion target than `T₂` ([§11.6.4.6](expressions.md#11646-better-conversion-target))
+- `E` is a method group ([§11.2](expressions.md#112-expression-classifications)), and `T₁` is compatible ([§19.4](delegates.md#194-delegate-compatibility)) with the single best method from the method group for conversion `C₁`
 
 #### 11.6.4.5 Exactly matching expression
 
@@ -1018,7 +1019,7 @@ Given an expression `E` and a type `T`, `E` ***exactly matches*** `T` if one of
 
 #### 11.6.4.6 Better conversion target
 
-Given an expression `E` and two types `T₁` and `T₂`, `T₁` is a ***better conversion target*** than `T₂` for `E` if one of the following holds:
+Given two types `T₁` and `T₂`, `T₁` is a ***better conversion target*** than `T₂` if one of the following holds:
 
 - An implicit conversion from `T₁` to `T₂` exists
 - `T₁` is `Task<S₁>`, `T₂` is `Task<S₂>`, and `S₁` is a better conversion target than `S₂`
@@ -1027,7 +1028,6 @@ Given an expression `E` and two types `T₁` and `T₂`, `T₁` is a ***better c
   - `S₁` is `short` and `S₂` is `ushort`, `uint`, or `ulong`
   - `S₁` is `int` and `S₂` is `uint`, or `ulong`
   - `S₁` is `long` and `S₂` is `ulong`
-- `E` is a method group conversion ([§10.8](conversions.md#108-method-group-conversions)) and `T₁` is compatible ([§19.4](delegates.md#194-delegate-compatibility)) with the single best method from the method group
 
 #### 11.6.4.7 Overloading in generic classes