ADR suggestion: Support Parameter dependencies in .min and .max

[henrikjacobsenfys]

It is very natural for users to want a Parameter to always be larger than a different Parameter. This would be done by setting e.g.

a=Parameter(name='a',value=1)
b=Parameter(name='b',value=2,min=a)

If a user (or a fit) then updates a, the min of b updates to the new value of a, If a.value>b.value, then b.value=a.value should be set.

Also posted as an issue: #192

[damskii9992]

To limit the scope of this feature request, we discussed and agreed that this requirement will initially only be equal to another Parameters value. I.e. we won't allow dependency expressions in the min and max.
Dependency expressions in the min and max can be implicitly implemented by making a new dependent Parameter, and then setting the min or max to the value of this interim Parameter.