cytoframe keyword access methods

These methods allow for direct insertion, deletion, or renaming of keywords in cytoframe objects.

cf_keyword_insert(cf, keyword, value)

cf_keyword_delete(cf, keyword)

cf_keyword_rename(cf, from, to)

Arguments

cf	a cytoframe
keyword	the keyword name to insert/delete/replace
value	the value to associate with the supplied keyword
from	the old keyword name (for renaming)
to	the new keyword name (for renamiing)