Rename "imps", "noimps" roots() preferences to "breaks", "nobreaks".

"imps" and "noimps" are still supported for backwards compatibility
(though I find it unlikely that very many people will be using these).

Closes #886.
Remove "imps" and "noimps" options entirely.

I was confused:  these never existed in v4 to begin with!  No need to
support them at all!
Fixes to CHEBTECH/ROOTS. Closes #751.
Merge branch 'fix-chebtech-roots' into development

Conflicts:
	tests/misc/test_hermpoly.m
Merge branch 'fix-roots-imps' into development