docs: document 3 undocumented public modules

Author: Oakchris1955

src/block_io.rs

@@ -69,6 +69,7 @@ impl<T: BlockWrite> BlockWrite for &mut T {
     }
 }
 
+/// The block I/O prelude
 pub mod prelude {
     pub use super::{BlockBase, BlockRead, BlockWrite};
 }

src/fat/mod.rs

@@ -3,6 +3,7 @@ pub(crate) mod dirinfo;
 pub(crate) mod fatentry;
 pub(crate) mod file;
 pub(crate) mod fs;
+/// FileSystem mount options-related structs & methods
 pub mod options;
 pub(crate) mod serde;
 pub(crate) mod types;

src/lib.rs

@@ -230,6 +230,7 @@ pub(crate) mod fat;
 pub(crate) mod log;
 mod path;
 pub(crate) mod storage;
+/// Time-related traits, constants and structs
 pub mod time;
 pub(crate) mod utils;