mkdir()'s parameter is named dir_path in the header and absolute_path in the source

[skipbit]

include/dross/platform/path.h:70 and :92 declare the parameter as dir_path; src/platform/path.cpp:10 and :15 define it as absolute_path.

The source name also overstates the requirement — mkdir() accepts a relative path and creates it relative to the working directory. Nothing forces it to be absolute.

Renaming the definitions to dir_path settles both.