Spec clarification: downloadable grammar cannot be used by ANTLR to generate a parser

The grammar available from [here (link at bottom of page)](https://github.com/dotnet/vblang/tree/master/spec) is supposed to be in ANTLR format. However, ANTLR reports many warnings and errors:

>warning(184): d:\Zev\Projects\vbnet-grammer\vb.g4:187:0: One of the token Keyword values unreachable. REM is always overlapped by token CommentMarker
> warning(184): d:\Zev\Projects\vbnet-grammer\vb.g4:485:0: One of the token CCBinaryOperator values unreachable. & is always overlapped by token LongTypeCharacter
> warning(184): d:\Zev\Projects\vbnet-grammer\vb.g4:1386:0: One of the token OverloadableOperator values unreachable. & is always overlapped by token LongTypeCharacter
> warning(184): d:\Zev\Projects\vbnet-grammer\vb.g4:238:0: One of the token BooleanLiteral values unreachable. False is always overlapped by token Keyword
> warning(184): d:\Zev\Projects\vbnet-grammer\vb.g4:238:0: One of the token BooleanLiteral values unreachable. True is always overlapped by token Keyword
> ...
> error(119): d:\Zev\Projects\vbnet-grammer\vb.g4::: The following sets of rules are mutually left-recursive [CCExpression, CCOperatorExpression] and [Expression, IsExpression, MemberAccessBase, DictionaryAccessExpression, InvocationExpression, IndexExpression, AdditionOperatorExpression, SubtractionOperatorExpression, MultiplicationOperatorExpression, FPDivisionOperatorExpression, IntegerDivisionOperatorExpression, ModuloOperatorExpression, ExponentOperatorExpression, RelationalOperatorExpression, LikeOperatorExpression, ConcatenationOperatorExpression, ShortCircuitLogicalOperatorExpression, LogicalOperatorExpression, ShiftOperatorExpression, XMLMemberAccessExpression, TypeExpression, MemberAccessExpression, OperatorExpression, ArithmeticOperatorExpression, DivisionOperatorExpression]

Since ANTLR is a standard format for defining language grammars, I suggest modifying the grammar to make it ANTLR4 compatible.

Alternatively, the format should not be described as ANTLR.