creddit: libreddit: Project-wide debug option

This patch expands the debug system to be a project-wide debug setup
instead of internal to each module. The basic idea is that
./include/debug.h is included by every module in every file and has
basic macros for DEBUG_PRINT. Each module takes the liberty of setting a
module name for itself for the debug log, as well as the FILE* to write
to. The actual used FILE* can be found in ./src/global.c, all the other
FILE* for the debug file in other modules gets set to the contents of
that one when the program starts and the log file is opened. (You could set
the different modules to write output to different files, but that's not the default)

This really should have been what was done before, as the original debug
system was limited to libreddit and would have required a separate similar
system for creddit. This change allows for each module to use the same
unified debug setup.