variable_id validation #73
Description
The motivation
As a validator, any variables with either an underscore or a hyphen in their name should fail. These can cause many kinds of downstream software to trip up, so users should just use camel case instead if they need.
The proposed solution
Add validation of variable names (hence variable_id).
Alternatives
Additional context
Original discussion here: PCMDI/input4MIPs_CVs#131 (comment)