Add a way to use latex symbols

[pokorj54]

Allow to write symbols with latex, for example:
× \times
∑ \sum

and so on.

There are two possible approaches:

• just replace the command with the appropriate symbol
  • limited to which things can be rendered.
• create an image and then share an image
  • it is not friendly towards text.¨
  • this can for example do another bot named MathBot.

Ideally, both would be implemented.