v2.2.0

New Features:

• Unit types and member functions are now constexpr and noexcept wherever possible.
• Added cpow<..>(), a constexpr power function.
• Added make_unit factory function.
• Added cmath hypot() function.
• Added optional definition to disable IOStream in embedded applications.

Improvements:

• New and improved pi constant
• units::time and std::chrono are now interoperable
• eliminated warnings on gcc when using -Wall -Wextra -pedantic