Todo: Support Form-filling

[dwarring]

After some experimentation, setting the form value is not enough to enter a displayable value (Acrobat Reader). Displays OK on Xpdf, Evince, but AR needs an Appearance. Perl 5 CAM PDF's CAM::PDF.fillFormFields() can be used as a reference implementation for this feature.

[dwarring]

If PDF form fields are appropriately structured and to spec, it's not necessary to rebuild the forms appearance (/AP entry), but some aren't. Considering something like:

$form.value(:reformat) = $v

The form appearance will be rebuilt, but current form is lost. Can be used to fix up dodgy forms.