Refactor md_enums

Refactor md_enums

The old enum handling caused clang-tidy to complain about the globally
defined symbols for the enum strings, and also violated type safety by
using the enums both as enumerations and integers.

Changed all exposed enum strings and their corresponding char arrays
to classes and enumeration arrays.

Used enumeration array in a few places where it made sense to me.

Was not able to get rid of some instances where the enum to integer
conversion was abused.

Moved enum reading template to header to have it available for reading
all enums.