Allow identifiers containing numbers.

Closes #258.

src/Markup/Perspex.Markup/Binding/Parsers/IdentifierParser.cs

@@ -44,7 +44,8 @@ namespace Perspex.Markup.Binding.Parsers
                 return cat == UnicodeCategory.NonSpacingMark ||
                        cat == UnicodeCategory.SpacingCombiningMark ||
                        cat == UnicodeCategory.ConnectorPunctuation ||
-                       cat == UnicodeCategory.Format;
+                       cat == UnicodeCategory.Format ||
+                       cat == UnicodeCategory.DecimalDigitNumber;
             }
         }
     }

tests/Perspex.Markup.UnitTests/Binding/ExpressionNodeBuilderTests.cs

@@ -26,6 +26,14 @@ namespace Perspex.Markup.UnitTests.Binding
             AssertIsProperty(result[0], "_Foo");
         }
 
+        [Fact]
+        public void Should_Build_Property_With_Digits()
+        {
+            var result = ToList(ExpressionNodeBuilder.Build("F0o"));
+
+            AssertIsProperty(result[0], "F0o");
+        }
+
         [Fact]
         public void Should_Build_Property_Chain()
         {