Bump smartdown version to 0.5.4
Return Money and Date objects from SPL plugins
Merge pull request #1187 from alphagov/smartdown-bump-date-format

Format dates and salaries plugin results
Fix lower earnings plugin to use 0.5.4 smartdown syntax
Merge pull request #1189 from alphagov/fix-lower-earnings-text

Fix lower earnings plugin to use 0.5.4 smartdown syntax