Data type: symbol font reference

--Overview--

A reference to a [[type:symbol font]].

In [[type:stylesheet]]s the symbol fonts are not included inline, instead they are referenced by their package name.

--Properties--
! Property		Type			Default			Description
| @name@		[[type:scriptable]] Name of a [[type:symbol font]]
			 			''required''		Name of the symbol font package to use (without the extension).
| @size@		[[type:double]]		12			Size in points to render the symbols with.
| @scale down to@	[[type:double]]		1			Minimum size in points to scale the size down to.
| @alignment@		[[type:alignment]]	@"middle center"@	Alignment of symbols in a line of text.

--Example--
>symbol font:
>	name: magic-mana-small
>	size: 10
>	alignment: top left
The name can be scripted:
>symbol font:
>	name: { if set.use_larga_mana_symbols then "magic-mana-large" else "magic-mana-small" }
>	size: 10
>	alignment: top left
