bookmarks: make bookmarks.comparebookmarks accept binary nodes (API)
Binary bookmark format should be used internally. It doesn't make sense to have
optional parameters `srchex` and `dsthex`. This patch removes them. It will
also be useful for `bookmarks` bundle2 part because unnecessary conversions
between hex and bin nodes will be avoided.
bookmarks: rename `compare()` to `comparebookmarks()` (API)
Next commit will remove optional parameters from `compare()` function.
Let's rename `compare()` to `comparebookmarks()` to avoid ambiguity from
callers from external extensions.