Fix text spans being too long (using end pos as length)

Upsilon/Parser/ExpressionSyntax/BinaryExpressionSyntax.cs

@@ -10,7 +10,7 @@ namespace Upsilon.Parser
             Left = left;
             Operator = @operator;
             Right = right;
-            Span = new TextSpan(left.Span.Start, right.Span.End);
+            Span = new TextSpan(left.Span.Start, right.Span.End - left.Span.Start);
         }
 
         public override SyntaxKind Kind => SyntaxKind.BinaryExpression;

Upsilon/Parser/StatementSyntax/AssignmentExpressionSyntax.cs

@@ -13,7 +13,7 @@ namespace Upsilon.Parser
             EqualsToken = equalsToken;
             Expression  = expression;
             var start = LocalToken?.Span.Start ?? Identifier.Span.Start;
-            Span = new TextSpan(start, Expression.Span.End);
+            Span = new TextSpan(start, Expression.Span.End - start);
         }
 
         public override SyntaxKind Kind => SyntaxKind.AssignmentStatement;

Upsilon/Parser/StatementSyntax/BlockStatementSyntax.cs

@@ -13,7 +13,7 @@ namespace Upsilon.Parser
             var first = statements.FirstOrDefault();
             var last = statements.LastOrDefault();
             if (first != null && last != null)
-                Span = new TextSpan(first.Span.Start, last.Span.End);
+                Span = new TextSpan(first.Span.Start, last.Span.End - first.Span.Start);
         }
 
         public ImmutableArray<StatementSyntax> Statements { get; }

Upsilon/Text/TextSpan.cs

@@ -11,5 +11,10 @@ namespace Upsilon.Text
         public int Start { get; }
         public int Length { get; }
         public int End => Start + Length;
+
+        public override string ToString()
+        {
+            return $"{Start} - {End}";
+        }
     }
 }