Vec class objects can now be constructed during compile-time
as constant expressions by calling Vec( T, ... ) constructors
or through brace-initialization.
Constant expression using fill constructor and nested vectors
of sizes greater than 4 are not supported yet.
Changes made to WrappedOperators.h for resolving overload
ambiguities in Vec construction and typecasting.
Appropriate test cases were added to UnitTestTypes.cxx.
Addresses issue #199.