Implement RFC 11: Redesigning Wasmtime's APIs (#2897)

Implement Wasmtime's new API as designed by RFC 11. This is quite a large commit which has had lots of discussion externally, so for more information it's best to read the RFC thread and the PR thread.

crates/runtime/src/traphandlers/windows.rs

@@ -6,7 +6,8 @@ use winapi::um::winnt::*;
 use winapi::vc::excpt::*;
 
 /// Function which may handle custom signals while processing traps.
-pub type SignalHandler<'a> = dyn Fn(winapi::um::winnt::PEXCEPTION_POINTERS) -> bool + 'a;
+pub type SignalHandler<'a> =
+    dyn Fn(winapi::um::winnt::PEXCEPTION_POINTERS) -> bool + Send + Sync + 'a;
 
 pub unsafe fn platform_init() {
     // our trap handler needs to go first, so that we can recover from