Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/lib/btree.c b/lib/btree.c
index c9c6f03..2a34392 100644
--- a/lib/btree.c
+++ b/lib/btree.c
@@ -11,7 +11,7 @@
  * see http://programming.kicks-ass.net/kernel-patches/vma_lookup/btree.patch
  *
  * A relatively simple B+Tree implementation.  I have written it as a learning
- * excercise to understand how B+Trees work.  Turned out to be useful as well.
+ * exercise to understand how B+Trees work.  Turned out to be useful as well.
  *
  * B+Trees can be used similar to Linux radix trees (which don't have anything
  * in common with textbook radix trees, beware).  Prerequisite for them working
@@ -541,7 +541,7 @@
 	int i, no_left, no_right;
 
 	if (fill == 0) {
-		/* Because we don't steal entries from a neigbour, this case
+		/* Because we don't steal entries from a neighbour, this case
 		 * can happen.  Parent node contains a single child, this
 		 * node, so merging with a sibling never happens.
 		 */