Fix assorted comment and documentation typos

Examples/python/callback/runme.py

@@ -42,7 +42,7 @@ print
 print "Adding and calling another Python callback"
 print "------------------------------------------"
 
-# Lets do the same but use the weak reference this time.
+# Let's do the same but use the weak reference this time.
 
 callback = PyCallback().__disown__()
 caller.setCallback(callback)

Examples/python/multimap/example.i

@@ -98,7 +98,7 @@ extern int count(char *bytes, int len, char c);
 /* This example shows how to wrap a function that mutates a string */
 
 /* Since str is modified, we make a copy of the Python object
-   so that we don't violate it's mutability */
+   so that we don't violate its mutability */
 
 %typemap(in) (char *str, int len) {
 %#if PY_VERSION_HEX >= 0x03000000