Add Explicit Hook Functions

[axtimhaus]

To allow giving lambda functions as explicit hook value.
Only on explicit hook values callability will be checked.
Allowed are parameterless functions and functions with one parameter (self).
So for example:

Profile.round(
    diameter=10e-3,
    density=lambda self: 7.85 / (1 + 3 * 1e-5 * self.temperature),
)