Accept a trailing space at end of PEM lines

With certs being copy-pasted from webmails and all, this will probably become
more and more common.
diff --git a/ChangeLog b/ChangeLog
index 243b865..e65c977 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -20,6 +20,7 @@
 Changes
    * Add SSL_MIN_DHM_BYTES configuration parameter in config.h to choose the
      minimum size of Diffie-Hellman parameters accepted by the client.
+   * The PEM parser now accepts a trailing space at end of lines (#226).
 
 = mbed TLS 1.3.11 released 2015-06-04