API documentation

[alexander-held]

As far as I can see, there is no API documentation hosted anywhere for func_adl. Having this would be useful, for example to understand where the func_adl_callable decorator described in https://github.com/iris-hep/func_adl#function-definitions is located (it was easy enough to find at the expected func_adl.func_adl_callable spot, but ideally API documentation would answer this question).

[RogerJanusiak]

This is in progress now: https://rogerjanusiak.github.io/func_adl/. This is an early version.