Move xml-escaping to separate step after plugin runs in Generator.
Update Entries plugin to return add modify ts in add ts header mode.
Update Generator to set post_updated from new entries_map modify_ts.
Simplify Tags cache entries_tags map, dropping unused mtime.
Remove xml_escape flags on flavours; always escape, choose via templates.
Various small fixes to get unit tests passing again.
Remove .gitignore files from unit test directories.
Minor fixes to expected atom files in tag unit tests.
Tweak Statik::Config to allow unset config items to override defaults.