Various doc improvements (#248)
- Rename all the ugly template parameters (too long and/or starting
with an underscore).
- Rename function parameters starting with an underscore.
- Extend the doc for many classes.
- Use LaTeX-style O(...) expressions only for the complicated ones.
- A lot of small unification changes.
- Small fixes.
- Some other improvements.

Improve timer and counter tests (#253)

- Do not print the output of counter_test.cc.
- Check the output of counter_test.cc.
- Shorten the running time of time_measure_test.cc.