Allow color to be specified for a font-based icon

[mojavelinux]

Allow the color attribute to be specified on the icon macro to control the color of the font. The color can be specified using any format that is permitted in the PDF theme file (see /~https://github.com/asciidoctor/asciidoctor-pdf/blob/master/docs/theming-guide.adoc#colors).

Example:

icon:heart[color=ff0000]
icon:heart[color="255,0,0"]
icon:heart[color="0,0.99,1,0"]

[mojavelinux]

Currently, the workaround is to use Prawn-specific markup to set the color:

+++<color rgb="ff0000">+++icon:heart[]+++</color>+++

[lit-uriy]

Why another attribute?
In the User manual (http://asciidoctor.org/docs/user-manual/#inline-icons) already provided color throw role, like this:

icon:tags[role="blue"] ruby, asciidoctor

My code:

WARNING: Этот WARNING.

Это icon:flag[role="red"] инлайн иконка с красным флажком, а эта icon:tags[role="blue"] с синим ярлыком

In HTML output icon with color and admonition with color,

but PDF output - admonition with color, icon - WITHOUT color

P.S. To avoid confusion in the attributes, it is better to use only one, of course, the attribute "color" is more obvious, but then you need to remove from the documentation the attribute "role" (to leave just for compatibility).

[mojavelinux]

I agree that a role (aka class) would be better. But that would mean we need to implement generic roles in the theme. We could make that part of this fix, or at least a simplified version of it (where we just look for the color).

[mojavelinux]

Something like this in the theme:

role:
  red: #ff0000

And this in the AsciiDoc:

icon:heart[role=red]

I'd be happy with that.

(I put the role under the role category so it doesn't conflict with other top-level category names).

[lit-uriy]

When can this feature appear in Asciidoctor-pdf?

[mojavelinux]

I've already scheduled it for the next alpha, so I will try to stick to that if I can. Right now I'm busy working on the next release of Asciidoctor core.

[lit-uriy]

mojavelinux, thank you

[mojavelinux]

Roles for inline elements are now supported. Now we just need to apply the role to the icon.