[Feature] Make the content of common a DLL.

Currently, the "common" part of the repo contains npp_debug.*. Among the functionality provided by npp_debug is the ability to output debug messages that are indented depending from which level of function guards the output function is called.
This functionality works as long as it's contained within a single exe or dll. The functionality breaks once it's called across dlls / exes since each compiled units contains its own debug output.
By having this functionality available from a 3rd party dll, all the compiled units would share the same debug output and indenting across dlls / exes becomes feasible.