VOLE 0.5.1 released

Version 0.5.1 of VOLE released.

Changes:

• renamed coercion level nonDestructiveTruncation to nonDestructiveCoercion
• added com_return_traits<float>
• added com_return_traits<double>
• changed behaviour for com_return_traits<bool>, com_return_traits<short>, com_return_traits<int>, com_return_traits<long>, com_return_traits<std::string> and com_return_traits<std::wstring>
• added test.unit.return_traits.builtins
• added test.unit.return_traits.std_types