Added new filter operator for adding prefixes and suffixes to titles; these new filter operators are useful in contexts where only a filter expression is allowed and where macro processing isn't allowed. The filters complement the existing remove suffix and prefix filter operators. (So much for the "filter" in filter operator.)
added documentation tiddlers for addprefix and addsuffix; updated
documentation tiddlers for prefix, suffix, removeprefix, removesuffix to
reference the new addprefix and addsuffix filter operators.
Merge pull request #928 from TheDiveO/filter-operators-addsufprefix

addprefix and addsuffix filter operators