Add "includeDirs" option to Swig Options object

[steevhise]

the Include tag should be able to find files in multiple places. The solution would seem to be a SwigOpts option that can accept a string or an array of strings for paths in which include would look for a file.

[cdaringe]

hi @steevhise! we might be open to that. however, my gut impression is that file collection/aggregation is something of a pre-processing step.

@paulcpederson @Lochlan thoughts?