DOC: fix a few typos in the documentation

This commit deals with a few misspells in the documentation.
diff --git a/doc/coding-style.txt b/doc/coding-style.txt
index d6998dd..5f252ed 100644
--- a/doc/coding-style.txt
+++ b/doc/coding-style.txt
@@ -525,7 +525,7 @@
 there are no parenthesis. Most people do not really care as long as what
 is written is unambiguous.
 
-Braces opening a block must be preceeded by one space unless the brace is
+Braces opening a block must be preceded by one space unless the brace is
 placed on the first column :
 
 Right :
@@ -811,7 +811,7 @@
   | if ((fd = open(file, O_RDONLY)) < 0)
   |         return -1;
 
-This is wrong. The man page says that -1 is returned if an error occured. It
+This is wrong. The man page says that -1 is returned if an error occurred. It
 does not suggest that any other negative value will be an error. It is possible
 that a few such issues have been left in existing code. They are bugs for which
 fixes are accepted, eventhough they're currently harmless since open() is not
@@ -853,7 +853,7 @@
 comma if it is planned that new elements might later be added, this will make
 later patches shorter. Conversely, if the last element is placed in order to
 get the number of possible values, it must not be followed by a comma and must
-be preceeded by a comment :
+be preceded by a comment :
 
   | enum {
   |         first = 0,