Use `mp-units` approach for storing complex units

[Logarithmus]

This will allow seamless combination of different base dimensions, e. g. Time with Angle, DigitalInfo (Byte & Bit) and also store only non-zero unit exponents, instead of ISQ. The motivation is explained in Extensibility and make_dimension sections of CppCon 2019 talk.

• store unit exponents in a recursive type-level HList (emulate missing variadic generics)
• implement sort for HList (bubble, selection or qsort)
• implement merge operation for 2 sorted HLists
• consolidate unit exponents of same dimension

Useful links:

• mp-units type list implementation
• Type-level bubble sort in Rust