Handle negative line numbers in error messages

[yuhan0]

(partially fixes) #3687
I took the opportunity to refactor some of the rx forms and add documentation, let me know if these should be separated out or squashed.

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If you're just starting out to hack on CIDER you might find this section of its
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[vemv]

LGTM - great work!

Did you check that there's coverage for all code paths in

1378a72 de162d5

?

[yuhan0]

Yup, the existing cider-clojure-runtime-error-regexp tests cover both those cases:

Execution error (ArithmeticException) at foo/foo (src/haystack/parser.cljc:4).
where either (ArithmeticException) or foo/foo may be missing