Improve documentation on Multiple File Import and add documentation on the JSL for this JMP platform.

[MathStatChem]

The Multiple File Import is very useful.  Using MFI using the GUI is documented in the "Using JMP" help:  https://www.jmp.com/support/help/en/16.1/#page/jmp/import-multiple-files.shtml#

, but it appears that that documentation is incomplete:  for instance, how to do multiple file import of JSON files with specific JSON settings is not well described.

Also please add JSL documentation in the JMP documentation and scripting index on all the messages and options/arguments for this platform.