cppiatools boot

Like we talked at wwx adding a tool "cppiatools boot" similar to nekotools boot would be really great.

I think the command `haxe -main Main -cpp my.exe -D cppia=exe` would be nice,
keep the current cppia define instead of adding a new one.

And there could be several possible value: exe to auto detect from host arch, or windows/linux/mac to force "cross compile".

And thanks to the new dll-less feature we'd get a single file executable in seconds.