Merge branch 'ralf/poison' into 'master'

theories/lang/heap.v

theories/lang/lang.v

theories/lang/lib/arc.v

theories/lang/lib/lock.v

theories/lang/lib/memcpy.v

theories/lang/lib/new_delete.v

theories/lang/lib/spawn.v

theories/lang/lib/swap.v

theories/lang/lifting.v

theories/lang/notation.v

theories/lang/proofmode.v

theories/typing/function.v

theories/typing/lib/arc.v

theories/typing/lib/panic.v

theories/typing/lib/rc/rc.v

theories/typing/lib/refcell/ref_code.v

theories/typing/lib/refcell/refcell_code.v

theories/typing/lib/refcell/refmut_code.v

theories/typing/own.v

theories/typing/programs.v