change IntoVal so that it is easier to use in specs

CHANGELOG.md

theories/heap_lang/lib/atomic_heap.v

theories/heap_lang/lib/par.v

theories/heap_lang/lib/spawn.v

theories/heap_lang/lifting.v

theories/heap_lang/tactics.v

theories/program_logic/language.v

theories/program_logic/lifting.v

theories/program_logic/ownp.v

theories/program_logic/total_lifting.v

theories/program_logic/total_weakestpre.v

theories/program_logic/weakestpre.v