Fix character font lock

[rvlo]

Characters escaped weren't being formatted correctly, as shown by the submitted test.

Example of code that wasn't being formatted:
["text" \, "other"]
(str \[ "inside" \])

---

Before submitting a PR mark the checkboxes for the items you've done (if you
think a checkbox does not apply, then leave it unchecked):

• The commits are consistent with our contribution guidelines.
• You've added tests (if possible) to cover your change(s). Bugfix, indentation, and font-lock tests are extremely important!
• You've run M-x checkdoc and fixed any warnings in the code you've written.
• You've updated the changelog (if adding/changing user-visible functionality).
• You've updated the readme (if adding/changing user-visible functionality).

Thanks!

[rvlo]

I also propose moving the lambda arguments regex below character literals, for handling \% correctly. Would there be any problems in doing so?

[bbatsov]

You'll have to check this. The font-locking logic is quite brittle.

The changes you proposed look reasonable. Please, mention the fix in the changelog.

[rvlo]

I added a test for the % character literal, moved the lambda arguments below character literals, added an entry to the changelog, rebased on master and squashed the commits.

[bbatsov]

Thanks!