Disconnects Store state fields from Compiler (#1761)

*  Moves CodeMemory, VMInterrupts and SignatureRegistry from Compiler
*  CompiledModule holds CodeMemory and GdbJitImageRegistration
*  Store keeps track of its JIT code
*  Makes "jit_int.rs" stuff Send+Sync
*  Adds the threads example.

crates/wast/src/wast.rs

@@ -84,7 +84,7 @@ impl WastContext {
     }
 
     fn instantiate(&mut self, module: &[u8]) -> Result<Outcome<Instance>> {
-        let module = Module::new(&self.store, module)?;
+        let module = Module::new(self.store.engine(), module)?;
         self.modules.push(module.clone());
         let instance = match self.linker.instantiate(&module) {
             Ok(i) => i,