idea: Add uncertainty and other information to Param

[ConnorStoneAstro]

If Param is to represent a parameter, there is other useful metadata such as the uncertainty, and the valid range. Having a valid range would allow for converting to a reparametrized space where all values from -inf to inf are valid.

[ConnorStoneAstro]

Another useful quantity would be units.

Possibly also a flag for if the parameter value is cyclic (like a rotation angle which would behave under modulo arithmetic)

[ConnorStoneAstro]

PR #3 adds valid, cyclic, and units

[ConnorStoneAstro]

The treatment of units would likely be problem specific. Users should maybe subclass the Param object to add it the way they like