Leverage C++17 features.

[ossama-othman]

Remove MaRC implementations of C++17 features such as MaRC::hypot(), MaRC::size() and MaRC::data().

Enable use of some C++17 features such as constexpr methods and std::is_nothrow_swappable<>.

[coveralls]

Pull Request Test Coverage Report for Build 2863557488

• 19 of 21 (90.48%) changed or added relevant lines in 8 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 90.091%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
lib/marc/BilinearInterpolation.cpp	0	1	0.0%
src/FITS_image_t.cpp	2	3	66.67%
<!--	Total:	19	21	90.48%	-->

Totals
Change from base Build 2862659212:	0.0%
Covered Lines:	3182
Relevant Lines:	3532

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💛 - Coveralls