add formatting support

[omnidan]

Telegram now supports simple markdown formatting: https://core.telegram.org/bots/api#using-markdown - we can use this to enable client.format.get('bold') (and italic and code)

Isn't this already implemented?

[omnidan]

@nyuszika7h only with telegram specific options - formatting should also be mapped by coffea so that it works the same way across platforms

I'm not sure if/how formatting is already implemented elsewhere in coffea, I didn't find anything regarding that with a quick grep in the core.

HTML would probably be better, it's more suited for things not directly exposed to users. Escaping Markdown with backslashes is possible, but it gets messy when you try to escape triple backticks for code blocks (though it seems to work, I don't remember what I had trouble with).

Maybe leave the default as plain text to avoid unexpected issues with special HTML characters, and use something like formatting: true to enable formatting:

reply({
  type: 'message',
  text: `Welcome, ${bold(name)}!`,
  formatting: true
})

And perhaps add an escapeHTML helper function. I use the xregexp module in my bot, but it's also possible with normal .replace().

export const escapeHTML = text =>
  XRegExp.replaceEach(text, [
    [/&/g, '&'],
    [/</g, '&lt;'],
    [/>/g, '&gt;'],
    [/'/g, '&#39;'],
    [/"/g, '&quot;'],
  ])

or

export const escapeHTML = text =>
  text.replace(/&/g, '&')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
    .replace(/'/g, '&#39;')
    .replace(/"/g, '&quot;')

(Note that Telegram doesn't support the named entity '. After escaping < and >, ' and " are probably safe, but it doesn't hurt to escape them anyway.)