add microturbulence to simulation

[jvshields]

There's also an option in the config to disable microturbulence.

Here's a solar spectrum of H-Alpha with microturbulence read from the Marcs model

Here's that with microturbulence disabled.

[andrewfullard]

Very cool, though your plot legend seems incorrect

[jvshields]

Tests fail because of the full regression test which needs new data, but I don't quite know how to do that yet and it will be in a different PR.