Add Structurizr DSL lexer

[vidbina]

• [x] Added thin as a dependency (needed this to spin up a local server for development)
• [x] Added test artifacts for the Structurizr DSL (basically copied as many examples from the docs into spec/visual/samples/structurizr to flag any errors that would pop up)
• [x] Defined lexer for Structurizr DSL

TL;DR

Used the Structurizr DSL original parser implementation as a bit of a guideline on how to order the state matchers and basically reduced my chain of arguably messy commits 🤷🏿 to provide a PR that is easier to review (hopefully). 😝

Let me know what needs fixing before this is remotely acceptable for a merge.

[vidbina]

Oopsie. 🤦🏿 67c7d01 fixes the tests that were breaking. Had a case of "works on my machine" for the test suite in my env. Now that the pipeline tests are green, I hope this inches a step closer towards getting a merge.

Let me know if something still falls short of the merge requirements.