Adjust start of bracket search in find* functions

Instead of adjusting the search position on the caller side, do it
within the functions. This makes the call sites more similiar, preparing
some code consilidation.
Change order of  'if' branches when handling ']' command

This makes the code for handling '[' and ']' more similiar, simplifying
code consolidation.
Renamed helper functions for handling '[' and ']' commands

The new term is more generic. By now the code for handling ']' and '['
is so similiar that it should be straightforward to merge it.
Resolved code duplication in handling of '[' and ']' commands

Turned out that these commands are very similiar, so we can merge them.
Resolve code duplication in handling '<' and '>'