Add sub/superscript and partial word emphasis

[vkbo]

Summary:

This PR:

• Extends the [command] and [command:value] used for new page and vertical space to also be used in-line in the text.
• Add formatting syntax for superscript and subscript using [sup][/sup] and [sub][/sub].
• Add partial word-capable format codes for bold, italic, underline and strikethrough using [b][/b], [i][/i], [u][/u] and [s][/s].

This format can also be extended for footnotes and endnotes, which are also planned features.

Related Issue(s):

Closes #1337
Closes #1444

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All flake8 checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed