Do The Right Thing with spaces around `ADDED` cohorts

[unhammer]

cf. giellalt/lang-smj#106 the rule writer shouldn't have to worry about spaces before/after added words.

Plan:

• when doing ADDCOHORT … ADDED, divvun-suggest should use a default rule that surrounds newly added words with spaces, except before/after certain punctuation (hardcoded)
• if the grammar writer needs more control, e.g. languages with special rules about punctuation-spacing or is adding punctuation, then we add more &TAG features to support this to divvun-suggest as needed