Add time units to time variables, functions.

Conflicts:
	src/config.hpp
	src/pool.cpp
	src/session.cpp
Make default logger print ms-since-epoch

Without getting into custom formats and timezone conversion for real
date/time formatting, this at least allows one to view relative times
for testing and troubleshooting.
Fix to work with different definitions of cass_uint64_t
Changed simultaneous->concurrent for config.

Also, spellcheck.
Merge pull request #77 from datastax/time-units

Time units and timestamp in default log callback