Rank sampling dens is now a template parameter

since we can not set the value of the
constructor parameter, when rrr_vector is
used in more complex classes. Now
You Get What You Declare :)
Fixed compile warning: signed/unsigned comparison.
Conversion to microseconds.
Added template argument.
Added checksum to prevent that the calls are

optimized away.
Removed unnecessary private keyword.
Removed unused parameter.
Removed unused parameter.
Merge pull request #83 from simongog/YGWYD_rrr_vector

Address issue #82 for rrr_vector