Allow passing arbitrary arguments for attributes to svg inliner

[wout]

Purpose

Makes it possible to add arbitrary attributes to inline SVGs.

Description

More than often I need to add attributes to inline SVGs, especially with ARIA, and sometimes class names or data attributes. Until now I've been adding them manually to the SVG source files, but it's easy to lose oversight and forget adding some attributes (like aria-hidden for example).

This PR makes it possible to add arbitrary attributes to the SVG tag:

inline_svg("some/icon.svg", aria_hidden: true, class: "icon")

It also still works with the strip styling flag:

inline_svg("some/icon.svg", false, data_very: "lucky")
# or
inline_svg("some/icon.svg", strip_styling: false, data_very: "lucky")

Finally something I wanted to add for a long time already, allowing to pass the file path without the extension:

inline_svg("some/icon")
# resolves to "some/icon.svg"

Checklist

• - An issue already exists detailing the issue/or feature request that this PR fixes
• - All specs are formatted with crystal tool format spec src
• - Inline documentation has been added and/or updated
• - Lucky builds on docker with ./script/setup
• - All builds and specs pass on docker with ./script/test

[jwoertink]

Nice!