Options page modernization

[wheelercj]

Currently, Stardown's settings page is very simple. I would like to keep it easy to use and lightweight, but there are many ways it could be improved.

For example, the options page could let users directly:

• report bugs
• request a feature
• donate

All without navigating to GitHub or another website.

[wheelercj]

In the future, settings for customizing markdown formatting will probably be added, such as:

• code block style: fenced or indented. If fenced, backticks or tildes.
• heading style: atx or setext
• bold style: ** or __
• italic style: * or _
• indent with 4 spaces or a \t
• inline links or reference links
• whether to convert superscripts like y^[1] to y[1] or y^[1]^, and subscripts like H₂O to H2O or H~2~O (the latter of each use the rarely supported markdown syntax explained in Extended Syntax | Markdown Guide)
• whether to align tables