some legacy gimp smc scripts ported to 3.x

[jkbzh]

Hi!

I ported some scripts that I had gotten off the registry in times gone past and which are part
of my workflow. I don't know if they are still being maintained and I contacted the authors
to see if I can send them the changes or if they moved on from them.

In the meantime, if you are using them or want to try them out, you can get them from this
github repo [1].

You can check them out on github. 

• silicosaur (Baráth Gábor) film effect filters (only works on 3.2 due to bug in 3.0 re spline-curves)
  

• silicosaur-photofx-velvia (Fujifilm Velvia 50)
  
• silicosaur-photofx-provia (Fujichrome Provia chrome)
  
• silicosaur-photofx-portra (Kodak Portra)
  
• silicosaur-photofx-crossprocess (Cross process (x-pro) effect)
  
•  Ryan Burnside filters for adding different kinds of guidelines (percent, golden-rule, centered,...)
  
  •  divide-thirds
    

The first commit I had made was the 2.10 version so you could see the changes to port them to 3.x. and use that as an example in porting other legacy scripts. Alas,  as I'm writing this, I realize that is lost in all but one plug-in because I squashed the branch commits for the other ones.

This was an interesting experience, learning scheme and GIMP plug-in's API.

Enjoy!

[1] https://github.com/jkbzh/gimp3-scm-plugins