Allowable characters in SDF defined terms

[mjkoster]

SDF Defined terms are JSON names (keys) and have some restrictions.

There needs to be a way to handle "/" in names when using the name in a JSON Pointer. JSON Pointer has a defined escape mechanism for this.

There needs to be an answer for space characters in names. We could not allow spaces in names, or we could define an escape mechanism for spaces also. It is suggested to reserve "_" to use in place of space.