Support struct/union/enum standalone declarations without body again
Add -inclib option to generate #inclib statements
Remove contrib/ presets

Presets are too situational. They should be included in the same repo as
the generated headers to allow those to be re-generated exactly.
Add -pragmaonce for emitting #pragma once statements
Add #include "crt/long.bi" if CLONG is used, etc.
Always enable all targets
Do version AST merging after all parsing has finished
Remove support for multiple root files & -common

i.e. root files won't be treated as separate APIs anymore.
The version-specific parsing process now produces one AST per version and
that's it. Easier to merge aswell. This also makes -common obsolete.
This matches the idea that fbfrog works like a compiler that creates one
binding for exactly the input it's given.
Remove useless presetcode <> NULL checks
Show help if no command line arguments given
Add support for simple __attribute__((packed))