Introduce common::memory

[schnellerhase]

Introduces free function common::memory. Which provides a unit based access (in B, KB, MB, ...) to the implementation detail common::impl::memory, which computes for given types the used memory in bytes. This needs to be implemented for every type of which one wants to have access to a memory consumption (and its member types!).

This provides a user controllable memory profiling capability, up to a desired/required precision.

First step towards #1741.

[schnellerhase]

This is not yet ready for a proper review, but before extending the interface to more heavy types I wanted to check if this was the right way to go about implementing this interface or if this approach misses some important capabilities we would like to see.

In particular the python side is still very rough, and something along the lines of https://github.com/timlnx/bitmath/, would be very desirable.