Updated operator<<() to make it more generic so it works for all quantities.
Operator << now writes directly to the specified output stream instead of using an ostringstream.
Added a file for holding fundamental physical constants.
Added units for permittivity and permeability.
PhysicalConstants.hpp now includes ScientificQuantities.hpp so that users may just include PhysicalConstants.hpp. This also makes PhysicalConstants.hpp self-sufficient.
Added alternate names for length units based on http://physics.nist.gov/cuu/Units/units.html.
Updated to define derived units in terms of base units instead of hard-coding the dimensions. Added the ability to define fundamental units of various quantities. Added the ability to print quantities with fundamental units and an overload that prints generic quantities that do not have any fundamental units.