Add missing error and panic docs

Author: madsmtm

src/block.rs

@@ -116,7 +116,7 @@ impl<A: BlockArguments, R: EncodeReturn> Block<A, R> {
         let ptr: *const Self = self;
         let layout = unsafe { ptr.cast::<ffi::Block_layout>().as_ref().unwrap_unchecked() };
         // TODO: Is `invoke` actually ever null?
-        let invoke = layout.invoke.unwrap();
+        let invoke = layout.invoke.unwrap_or_else(|| unreachable!());
 
         unsafe { A::__call_block(invoke, ptr as *mut Self, args) }
     }

src/lib.rs

@@ -84,6 +84,8 @@
 #![deny(unsafe_op_in_unsafe_fn)]
 #![warn(clippy::cargo)]
 #![warn(clippy::ptr_as_ptr)]
+#![warn(clippy::missing_errors_doc)]
+#![warn(clippy::missing_panics_doc)]
 // Update in Cargo.toml as well.
 #![doc(html_root_url = "https://docs.rs/block2/0.3.0")]