* Avoid inline styles inside `<code>` / `<pre>` conversion

The check used for this is analogous to that used to avoid escaping
potential markup characters inside such tags.

Fixes #103

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Co-authored-by: AlexVonB <[email protected]>

* Escape all characters with Markdown significance

There are many punctuation characters that sometimes have significance
in Markdown; more systematically escape them all (based on a new
escape_misc configuration option).

A limited attempt is made to limit the escaping of '.' and ')' to the
context where they might have Markdown significance (after a number,
where they can indicate an ordered list item); no such attempt is made
for the other characters (and even that limiting of '.' and ')' may
not be entirely safe in all cases, as it's possible the HTML could
have the number outside the block being escaped in one go,
e.g. `<span>1</span>.`.

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Co-authored-by: AlexVonB <[email protected]>

see badges/shields#8671

fixes #126

Allow different strings before / after `<sub>` / `<sup>` content

In particular, this allows setting `sub_symbol='<sub>'`,
`sup_symbol='<sup>'`, to use raw HTML in the output when
converting subscripts and superscripts.

Co-authored-by: Mico <[email protected]>