Extensions

Extensions comprise an About.ey descriptor, and at least one of an
include.h header, an implement.h header, or a Makefile.

Typical About.ey:

%E-YAML
---

Name: Timelines
ID: Timelines
Depends: None
Dependencies: None
Description: Adds the timeline variables.
Implements: extension_timelines

Typical implement.h:

namespace enigma {
  struct extension_path
  {
    int path_endaction;
    int path_index;
    bool path_orientation;
    double path_position;
    double path_positionprevious;
    double path_scale;
    double path_speed;
  };
}

include.h will simply be included from SHELLmain.cpp, and can contain
anything necessary. The makefile isn't invoked at the moment, so I'll
get back to you on its spec.