Refs #10028.  Solved one issue in filtering by single value.

Issue: it was not considered about how to deal with the situation that
if two adjacent log entries' values are identical.

The new algorithm is to extend the previous direction.
Refactored codes to identify log value. Refs #10028.
Rewrote the method. Refs #10028.
Solved some issues about log boundary. Refs #10028.
Corrected unit tests. Refs #10028.
Improved doc. Refs #10028.
Refs #10028.  Corrected an error for integer log.

The correction to unit test was made as well.
The documentation is modified for integer sample log.
Merge branch 'bugfix/10028_generate_filter_direction' into develop