[RFC] Let's learn basic arithmetics!

[angeloreale]

Let's validate user input for basic arithmetics operators (+, -, *, /) on number values text inputs and cast them to a final number!

• (optional) As a plus, let's allow them to @ reference another field in the same dataset!
• (optional) As a plus, let's allow them to @ reference another field in a different dataset!

[angeloreale]

I'll be working on those, that's why I'm not writing a full spec. This is to track.