v13.0.0

This release moves to a new majour number because :

1. we are using a new library for command line parsing : CLI11
2. we now support the standard --long form of CLI arguments
3. underscores in long arguments have been replaced by dashes : eg -force_rgb has changed to --force-rgb
4. only lower case letters are used in long arguments
5. we have also enforced snake case for all variables in grok.h header

In other words, many CLI arguments and interface variables have changed. Please bear with us while we make the Grok API more expressive and easier to use.

The other majour feature in this release is new Rust bindings for Grok.