Added a few missing primitive parsers

src/Discord.Net.Commands/PrimitiveParsers.cs

@@ -22,6 +22,9 @@ namespace Discord.Commands
             parserBuilder[typeof(uint)] = (TryParseDelegate<uint>)uint.TryParse;
             parserBuilder[typeof(long)] = (TryParseDelegate<long>)long.TryParse;
             parserBuilder[typeof(ulong)] = (TryParseDelegate<ulong>)ulong.TryParse;
+            parserBuilder[typeof(float)] = (TryParseDelegate<float>)float.TryParse;
+            parserBuilder[typeof(double)] = (TryParseDelegate<double>)double.TryParse;
+            parserBuilder[typeof(decimal)] = (TryParseDelegate<decimal>)decimal.TryParse;
             parserBuilder[typeof(DateTime)] = (TryParseDelegate<DateTime>)DateTime.TryParse;
             parserBuilder[typeof(DateTimeOffset)] = (TryParseDelegate<DateTimeOffset>)DateTimeOffset.TryParse;
             _parsers = parserBuilder.ToImmutable();