Proguard renaming of TimeUnit classes can lead to MissingResourceException: Can't find resource for bundle org.ocpsoft.prettytime.i18n.Resources, key ePattern

The bundled proguard rules only keep org.ocpsoft.prettytime.i18n but some ResourceBundle classes rely on TimeUnit.getClass().getSimpleName() which are in org.ocpsoft.prettytime.units and thus allowed to be renamed by proguard.

For example

prettytime/core/src/main/java/org/ocpsoft/prettytime/i18n/Resources_de.java

Line 133 in 3c2206d

return new DeTimeFormat(this, t, t.getClass().getSimpleName());

Solutions I can think of are
Refactor code to not use TimeUnit.getClass().getSimpleName(), it looks like ResourcesTimeUnit.getResourceKeyPrefix() is appropriate but it's not on TimeUnit directly
Update proguard rules to keepnames for org.ocpsoft.prettytime.units, this is easiest to do but feels less than idea. It also slightly feels like it's covering up a deeper problem.

Relevant stack trace

java.util.MissingResourceException: Can't find resource for bundle org.ocpsoft.prettytime.i18n.Resources, key ePattern
        at java.util.ResourceBundle.getObject(ResourceBundle.java:445)
        at java.util.ResourceBundle.getObject(ResourceBundle.java:439)
        at java.util.ResourceBundle.getString(ResourceBundle.java:402)
        at org.ocpsoft.prettytime.i18n.Resources_de$DeTimeFormat.<init>(Resources_de:141)
        at org.ocpsoft.prettytime.i18n.Resources_de.getFormatFor(Resources_de:133)
        at org.ocpsoft.prettytime.impl.ResourcesTimeFormat.setLocale(ResourcesTimeFormat:52)
        at org.ocpsoft.prettytime.impl.ResourcesTimeFormat.setLocale(ResourcesTimeFormat:15)
        at org.ocpsoft.prettytime.PrettyTime.registerUnit(PrettyTime:1473)
        at org.ocpsoft.prettytime.PrettyTime.addUnit(PrettyTime:1613)
        at org.ocpsoft.prettytime.PrettyTime.initTimeUnits(PrettyTime:1597)
        at org.ocpsoft.prettytime.PrettyTime.<init>(PrettyTime:98)
        at org.ocpsoft.prettytime.PrettyTime.<init>(PrettyTime:86)
        ```

Same issue

Happy to accept a PR for these issues. Thanks!