Minor: Update copyright year

Bump version number to 5.3

Minor: Update copyright year in the license

Bump version number to 5.1

Fix inconsistent directory separators in the autoloader.

It looks like this was the cause of a version 5.0 bug reported in #378.

Bump version to 4.13

Also updated the POT file. No new strings, but some of the source code references were out of date.

Rename classes for 4.12

Change version number in file/directory names

Step 2 of version bump

Minor: Fix incorrect version number in a doc-comment

Bump version number to 4.9