[#119] Support link blocks

[dcastro]

Description

Problem: If a user types a message with a link, the link text will be ignored by the MessageBlock processor:

For example, in the message below, extractPieces will return ["Hey let's meet at ", "tomorrow?"].

Hey, let's meet at [10:30](link to google calendar here) tomorrow?

Solution: Parse blocks of type link, and collate the link text with adjacent text-like blocks.

Related issue(s)

Fixed #119

:white_check_mark: Checklist for your Pull Request

Related changes (conditional)

• Tests

  • [x] If I added new functionality, I added tests covering it.
  • [x] If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • [x] I checked whether I should update the docs and did so if necessary:
  • README
  • Haddock

Stylistic guide (mandatory)

• [x] My commits comply with the policy used in Serokell.
• [x] My code complies with the style guide.

✓ Release Checklist

• [ ] I updated the version number in package.yaml.
• [ ] (After merging) I created a new entry in the releases page, with a summary of all user-facing changes.
  • I made sure a tag was created using the format vX.Y