Fix number parsing

[JohnBrinkman]

The grammar correctly defines the construction of numbers, however the implementation doesn't follow the grammar rules. Examples:

Expression	current result	expected
3e+	3	error
3e	3	error
3.	3	error
3.e2	300	null (the ".e2" should be a chained expression)
3.toString(@)	syntax error	"3"
3.2.toString(@)	syntax error	"3.2"