Missing tests for spec sections 5.13 and 5.14 (Escaped Characters)

[andrewhickman]

Most of the examples from the spec are included as tests, but I notice 5.13 and 5.14 are absent.

In particular, I don't see any test in this suite which uses escaped 32-bit unicode characters like "\U00000041"

I'm happy to submit a PR, but I'm not sure how these test files are generated. Are the tree/dump/emit fields just handwritten?

[perlpunk]

I think for the current format we don't have a tool right now.
We used a tool when the test files were still using the tml format.
Maybe @ingydotnet knows a way?

[ingydotnet]

make new-test