Search by `kind` functionality needed.

[DavidSagan]

Prototype:

search(root_node, kind_type_string)

For example with:

Q1:
   kind: Quadrupole

A search with kind_type_string equal to "Quadrupole" could be used to search for all Quadrupole instances and return an array of pointers to the elements (in this case the Q1 node) of the given kind.

Note: Ultimately, this functionality will need to be generalized so that other parameters can be searched for.