Allow ability to use default width when adding align/description

[Whiteknight]

The arguments to the #ev and #evp tags are positional, so a width must be provided if an align and description are required. Some ways around this:

• Create a new tag (#embedvideo?) that takes named parameters
• The #ev and #evp tags do some pattern matching to automatically assign out-of-order positionals ("right"/"left" is always the alignment, the width is always numerical, the description is textual and neither of the other two, etc).
• Allow the width to be blank, or be a perl6esque "whatever star"

[Whiteknight]

Fixed