versioning C++ data structure to maintain back-compatibility when the class evolves

[mikejiang]

Since we've added the new data members to c++ classes from two major enhancements in #79 and #35 , it would be helpful to use boost serialization versioning mechanism to be able to load the old archives without having to reprocess the raw data.

[mikejiang]

Regarding to the issue of using float instead of double, it mainly involves the gate coordinates and calibration tables in c++ data structure.(flow data is already represented as float type in ncdfFlow).
Since calibration tables are now stored globally, double type should be fine at this point.
In order to read the old archives created before, I reverted the 270d31c for now. We can come back to restore this commit later on when necessary.