feat: add marko language

[manan-gup]

Added Marko language from eBay's Marko web framework

e.g.

<await(slowPromise) timeout=5000>
  <@then>Done</@then>
  <@catch|err|>
    <if(err.name === "TimeoutError")>
      Took too long to fetch the data!
    </if>
    <else>
      Promise failed with ${err.message}.
    </else>
  </@catch>
</await>

• Add a test if possible
• Format all commit messages with Conventional Commits

• I have read docs for adding a language.
• I have searched around and this is the most up-to-date, actively maintained version of the language grammar.
• I have added a sample file that includes a variety of language syntaxes and succinctly captures the idiosyncrasy of a language. See docs for requirement.

[octref]

Great work, thanks!

[manan-gup]

Thanks, happy to help.