allow variable names to contain numbers

[JJBordy]

Unfortunately it gives an error if I try to pass a variable name which has a number in it; For example, a map with {"catX":"33"} evaluates fine; but if I pass: {"cat1":"33"} it says that there is no such variable "cat", ignoring the number in the name

if there is no way to solve this, maybe indicate that in the "readme" file