Expand documentation with examples section

[francisrstokes]

To aid in showing how Super Expressive can be used in a practical context, it would be nice add an examples folder, with various common regex use cases.

• [ ] Using string.replace (#5)
• [ ] Using string.match to capture information
  • [ ] Indexed groups
  • [ ] Named groups
• [ ] Code organisation with subexpressions

Each example should be a separate .md document, with a title, short introduction, some commented example code, and related links sections (to things like MDN, or regex101). The examples folder should contain an index.md that acts as the contents page - linking to each example with a one sentence description.