Reorganize tests (#523)

* Refactor Lightbeam's tests.

This refactors Lightbeam's tests.rs file into several pieces, separating
quickcheck tests into their own file, and moving tests which can be run as
wast tests into `tests/misc_testsuite`, and creating a tests directory
for the rest.

* Remove the old filetests tests.

These are all covered by misc_testsuite and spec_testsuite tests.

* rustfmt

* Remove the "bench" feature.

crates/lightbeam/tests/wrongs.rs

@@ -0,0 +1,45 @@
+use lightbeam::{translate, ExecutableModule, ExecutionError};
+
+fn translate_wat(wat: &str) -> ExecutableModule {
+    let wasm = wat::parse_str(wat).unwrap();
+    let compiled = translate(&wasm).unwrap();
+    compiled
+}
+
+#[test]
+fn wrong_type() {
+    let code = r#"
+(module
+  (func (param i32) (param i64) (result i32)
+    (i32.const 228)
+  )
+)
+    "#;
+
+    let translated = translate_wat(code);
+    assert_eq!(
+        translated
+            .execute_func::<_, ()>(0, (0u32, 0u32))
+            .unwrap_err(),
+        ExecutionError::TypeMismatch
+    );
+}
+
+#[test]
+fn wrong_index() {
+    let code = r#"
+(module
+  (func (param i32) (param i64) (result i32)
+    (i32.const 228)
+  )
+)
+    "#;
+
+    let translated = translate_wat(code);
+    assert_eq!(
+        translated
+            .execute_func::<_, ()>(10, (0u32, 0u32))
+            .unwrap_err(),
+        ExecutionError::FuncIndexOutOfBounds
+    );
+}