Add XML-ish example

[anko]

Add an example parser of a subset of XML, as @wavebeem suggested. I tried to follow the style of other examples.

It seems the changelog hasn't mentioned addition of previous usage examples either, so I didn't touch it.

• I have run npm run lint:fix to ensure Prettier and ESLint have passed
• Coveralls bot has replied that the tests pass with 100% code coverage (npm test)
• I have updated CHANGELOG.md

[coveralls]

Coverage remained the same at 100.0% when pulling 063cbb6 on anko:xmlish-example into 62f9b15 on jneen:master.

[wavebeem]

Good call; examples don't need to go in the changelog :) Thanks for submitting this PR