1.11

Around 85 commits, most of which are porting from nasm-segelf to nasm.

• nasm-segelf no longer needed, code fully ported to nasm+manual relocs.
• lld can now be used w/o sacrificing ~8K of DOS memory space.
• int32 handler rewritten to not run its code on stack
• added int21/8Ch call: SET SIGNAL HANDLER
• hmamgr: implement topdown allocations
• deb packages split to separate lib* packages
• Replace prf.c with new printf implementation (@andrewbird)
• switch to c++20 for concepts and lambdas (Focal build dropped)