Make futures make sense independently of streams (#524)

Author: lukewagner

design/mvp/Async.md

@@ -619,7 +619,7 @@ Despite the above, the following scenarios do behave deterministically:
   that was blocked before starting due to backpressure, cancellation completes
   deterministically and immediately.
 * When both ends of a stream or future are owned by wasm components, the
-  behavior of all read, write, cancel and close operations is deterministic
+  behavior of all read, write, cancel and drop operations is deterministic
   (modulo any nondeterminitic execution that determines the ordering in which
   the operations are performed).
 

design/mvp/Binary.md

@@ -302,15 +302,15 @@ canon    ::= 0x00 0x00 f:<core:funcidx> opts:<opts> ft:<typeidx> => (canon lift
            | 0x10 t:<typeidx> opts:<opts>                        => (canon stream.write t opts (core func)) 🔀
            | 0x11 t:<typeidx> async?:<async?>                    => (canon stream.cancel-read async? (core func)) 🔀
            | 0x12 t:<typeidx> async?:<async?>                    => (canon stream.cancel-write async? (core func)) 🔀
-           | 0x13 t:<typeidx>                                    => (canon stream.close-readable t (core func)) 🔀
-           | 0x14 t:<typeidx>                                    => (canon stream.close-writable t (core func)) 🔀
+           | 0x13 t:<typeidx>                                    => (canon stream.drop-readable t (core func)) 🔀
+           | 0x14 t:<typeidx>                                    => (canon stream.drop-writable t (core func)) 🔀
            | 0x15 t:<typeidx>                                    => (canon future.new t (core func)) 🔀
            | 0x16 t:<typeidx> opts:<opts>                        => (canon future.read t opts (core func)) 🔀
            | 0x17 t:<typeidx> opts:<opts>                        => (canon future.write t opts (core func)) 🔀
            | 0x18 t:<typeidx> async?:<async?>                    => (canon future.cancel-read async? (core func)) 🔀
            | 0x19 t:<typeidx> async?:<async?>                    => (canon future.cancel-write async? (core func)) 🔀
-           | 0x1a t:<typeidx>                                    => (canon future.close-readable t (core func)) 🔀
-           | 0x1b t:<typeidx>                                    => (canon future.close-writable t (core func)) 🔀
+           | 0x1a t:<typeidx>                                    => (canon future.drop-readable t (core func)) 🔀
+           | 0x1b t:<typeidx>                                    => (canon future.drop-writable t (core func)) 🔀
            | 0x1c opts:<opts>                                    => (canon error-context.new opts (core func)) 📝
            | 0x1d opts:<opts>                                    => (canon error-context.debug-message opts (core func)) 📝
            | 0x1e                                                => (canon error-context.drop (core func)) 📝