Document all v14, v13 and most of v8 items (#33)

* Document all v14, v13 and most of v8 items

* Clarify what a `StorageEntryModifier` is.

frame-metadata/src/v10.rs

@@ -18,6 +18,8 @@
 //! Metadata Version 10. Networks like Kusama contain this version on-chain.
 //! Chains old enough to contain this metadata need a way to decode it.
 
+#![allow(missing_docs)]
+
 use crate::decode_different::*;
 use codec::{Encode, Output};
 
@@ -195,7 +197,11 @@ pub enum StorageEntryType {
 	},
 }
 
-/// A storage entry modifier.
+/// A storage entry modifier indicates how a storage entry is returned when fetched and what the value will be if the key is not present.
+/// Specifically this refers to the "return type" when fetching a storage entry, and what the value will be if the key is not present.
+///
+/// `Optional` means you should expect an `Option<T>`, with `None` returned if the key is not present.
+/// `Default` means you should expect a `T` with the default value of default if the key is not present.
 #[derive(Clone, PartialEq, Eq, Encode)]
 #[cfg_attr(feature = "std", derive(Decode, Serialize, Debug))]
 pub enum StorageEntryModifier {