Fix typos in code comments

Signed-off-by: Bisheng Huang <hbisheng@gmail.com>

examples/five_mem_node/main.rs

@@ -105,7 +105,7 @@ fn main() {
                 &logger,
             );
 
-            // Check control signals from
+            // Check control signals from the main thread.
             if check_signals(&rx_stop_clone) {
                 return;
             };

src/raw_node.rs

@@ -350,7 +350,7 @@ impl<T: Storage> RawNode<T> {
         self.raft.step(m)
     }
 
-    /// Propose proposes data be appended to the raft log.
+    /// Propose proposes data to be appended to the raft log.
     pub fn propose(&mut self, context: Vec<u8>, data: Vec<u8>) -> Result<()> {
         let mut m = Message::default();
         m.set_msg_type(MessageType::MsgPropose);
@@ -648,7 +648,7 @@ impl<T: Storage> RawNode<T> {
     /// committed entries, send all messages.
     ///
     /// Returns the LightReady that contains commit index, committed entries and messages. [`LightReady`]
-    /// contains updates that only valid after persisting last ready. It should also be fully processed.
+    /// contains updates that are only valid after persisting last ready. It should also be fully processed.
     /// Then [`Self::advance_apply`] or [`Self::advance_apply_to`] should be used later to update applying
     /// progress.
     pub fn advance(&mut self, rd: Ready) -> LightReady {

src/storage.rs

@@ -154,7 +154,7 @@ pub trait Storage {
     /// If snapshot is temporarily unavailable, it should return SnapshotTemporarilyUnavailable,
     /// so raft state machine could know that Storage needs some time to prepare
     /// snapshot and call snapshot later.
-    /// A snapshot's index must not less than the `request_index`.
+    /// A snapshot's index must not be less than the `request_index`.
     /// `to` indicates which peer is requesting the snapshot.
     fn snapshot(&self, request_index: u64, to: u64) -> Result<Snapshot>;
 }
@@ -373,7 +373,7 @@ impl MemStorageCore {
 /// `MemStorage` is a thread-safe but incomplete implementation of `Storage`, mainly for tests.
 ///
 /// A real `Storage` should save both raft logs and applied data. However `MemStorage` only
-/// contains raft logs. So you can call `MemStorage::append` to persist new received unstable raft
+/// contains raft logs. So you can call `MemStorage::append` to persist newly received unstable raft
 /// logs and then access them with `Storage` APIs. The only exception is `Storage::snapshot`. There
 /// is no data in `Snapshot` returned by `MemStorage::snapshot` because applied data is not stored
 /// in `MemStorage`.