cpp-argparse -> argtable
(mostly) rewrite in C
reorganize the frame interface
engine: revamp API, drop old implementation

API is in quite good shape, but the implementation
has to be redone from scratch.
fix stupid compilation glitch
typo
add vim footer
scripting: simplify the public API.
C99/compiler fixes
API fixes
scripting: port implementation to C

many GAPS still to be filled. JSON export missing.
API stubs