Modernise intrinsic update process

[gnikit]

Is your feature request related to a problem? Please describe. The current update process follows a CLI with poor interface options. I do not think that this is the best approach, since this part of fortls is untested and rather junky.

Describe the solution you'd like This should probably be a standalone tool external to fortls module or be properly incorporated into the module; unit tested and following good practices.