Expose marked options through SnapshotParserOptions

[codedevote]

Hi,

first of all thanks for this great library.
I was looking for options to influence the markdown rendering (in streaming mode) and as far as I understand the code, it might be an option to expose the marked options used in SnapshotParser class through the SnsapshotParserOptions.
I could then provide my own marked options and make use of the renderer (https://marked.js.org/using_advanced#options) to adjust markdown rendering to my needs.
What do you think? I could send a PR, if this makes any sense.