Added getTimeBaseIndices(name, tBegin, tEnd) which returns the k1, k2
indices corresponding to the specified times.

Added tBegin and tEnd keywords to getTimeBase. If not specified the
whole timebase will be  returned. If specified only the indices within
the interval are returned.
Merge pull request #14 from BSieglin/master

Added getTimeBaseIndices(name, tBegin, tEnd) which returns the k1, k2