Add increase/decrease command

[mwestphal]

Is your feature request related to a problem? Please describe. There are more and more dedicated increase_ commands in libf3d, we should hare a generic command that supports increasing/decreasing int and double options, which would let users define their own bindings for many more options.

This may require https://github.com/f3d-app/f3d/issues/2334

Describe the solution you'd like

• Improvement to option framework to specify a delta by option for increase/decrease
• A new method options::increase(double mult)
• A new command increase option mult