Add radio buttons, and changes styling of form

Fixes #27
BP-DATE(1980-04-03,%%m-%%e&%%Y)

change `%%.(1980-04-03)` into
`BP-DATE(<date>, <string with strtotime placeholders>)`
`BP-DATE(<date>, dformat)` prints the date in the format given by the
dformat config setting

Improves #36 and #28 further