Add option to control emission of noload segment

[polybiusproxy]

Adds option to control the emission of the .noload segment. Defaults to true.
Documentation hasn't been added yet.

[AngheloAlf]

I like the idea of avoid emitting all the stuff from the noload segment, including linker symbols and such, but I'm not so sure about making it a new setting because you can end up with a list of sections in noload_sections but emit_noload_segment: False which may be counterintuitive to the user.

Maybe we could make noload_sections nullable instead, so if you don't want those to get emitted then you would just do noload_sections: null instead of noload_sections: [] & emit_noload_segment: False