Fix typos in the documentation.

docs/protocol.txt

@@ -51,7 +51,7 @@ The server tells the client what refs it has. The client states which of those
 SHA1's it would like. It then starts to report which SHA1's it has. The server
 ACKs these allowing the client to work out when to stop sending SHA1's. This
 saves a lot of transfer because the client can make decisions like "well if it
-has this SHA, then it has all its parents so i dont need to care about those".
+has this SHA, then it has all its parents so I don't need to care about those".
 When the client stops sending shas, the server can work out an optimal pack and
 then send it to the client.
 

docs/tutorial/file-format.txt

@@ -36,7 +36,7 @@ A commit file looks like this::
  
   <commit message>
 
-But where are the changes you commited? The commit contains a reference to a
+But where are the changes you committed? The commit contains a reference to a
 tree.
 
 The Tree
@@ -63,7 +63,7 @@ content yet. That's where the reference to a blob comes in.
 The Blob
 --------
 
-A blob is simply the content of files you are versionning.
+A blob is simply the content of files you are versioning.
 
 A blob file looks like this::
 

docs/tutorial/object-store.txt

@@ -22,7 +22,7 @@ empty for now, we'll start by adding a new file::
 Of course you could create a blob from an existing file using ``from_file``
 instead.
 
-As said in the introduction, file content is separed from file name. Let's
+As said in the introduction, file content is separated from file name. Let's
 give this content a name::
 
   >>> from dulwich.objects import Tree

docs/tutorial/repo.txt

@@ -30,7 +30,7 @@ Let's create a folder and turn it into a repository, like ``git init`` would::
   >>> repo
   <Repo at 'myrepo'>
 
-You can already look a the structure of the "myrepo/.git" folder, though it
+You can already look at the structure of the "myrepo/.git" folder, though it
 is mostly empty for now.
 
 Opening an existing repository