sh.lang: Improve "here-doc" and array definition/expansion
-
here-doc
:- body text is subject to expansion when the here-doc-bound is unquoted
- a rest of line (to be highlighted normally) can be inserted between the first here-doc-bound and the body text
- When defining/expanding arrays, highlighting rules between square brackets are the same as in
arithmetic-expansion
- Also completes the list of bash built-in commands, transferring some from "common" to "built-in"