Make 'async' part of the function type, not a hint

Author: lukewagner

design/mvp/Binary.md

@@ -216,6 +216,7 @@ valtype       ::= i:<typeidx>                             => i
 resourcetype  ::= 0x3f 0x7f f?:<funcidx>?                 => (resource (rep i32) (dtor f)?)
                 | 0x3e 0x7f f:<funcidx> cb?:<funcidx>?    => (resource (rep i32) (dtor async f (callback cb)?)) 🚝
 functype      ::= 0x40 ps:<paramlist> rs:<resultlist>     => (func ps rs)
+                | 0x43 ps:<paramlist> rs:<resultlist>     => (func async ps rs)
 paramlist     ::= lt*:vec(<labelvaltype>)                 => (param lt)*
 resultlist    ::= 0x00 t:<valtype>                        => (result t)
                 | 0x01 0x00                               =>
@@ -288,7 +289,6 @@ canon    ::= 0x00 0x00 f:<core:funcidx> opts:<opts> ft:<typeidx> => (canon lift
            | 0x01 0x00 f:<funcidx> opts:<opts>                   => (canon lower f opts (core func))
            | 0x02 rt:<typeidx>                                   => (canon resource.new rt (core func))
            | 0x03 rt:<typeidx>                                   => (canon resource.drop rt (core func))
-           | 0x07 rt:<typeidx>                                   => (canon resource.drop rt async (core func)) 🚝
            | 0x04 rt:<typeidx>                                   => (canon resource.rep rt (core func))
            | 0x08                                                => (canon backpressure.set (core func)) 🔀✕
            | 0x24                                                => (canon backpressure.inc (core func)) 🔀