Restyle mapbuffer.cpp and mapbuffer.h
Move assure_dir_exist() to its own module.
Refactor submap saving and loading to write to individual files in preparation for saving/loading on-demand.
Automatically save submaps using new format when we load it from the old format.
Actually add the files that were supposed to be added in 0b2b2ff1
Extract coordinate translations to a helper method.
Remove an unnecessary multiplier on overmap coordintes used for save file names.
Extract conversion keys to the mapbuffer class.
Load submaps from disk on-demand.
Only load all submaps at game start if we hit a new version and we have to do a conversion.
Suppress map load progress message unless we're bulk loading for version conversion.
Bump map version number.
Move dynamic load code to the LOADING method, not the SAVING method.
Bring up to dae with upstream.
Fix moronic typo that prevented new maps from being generated.
Only display submap save/load popups if we're saving or loading a lot of submaps at once.
Throw away submaps after loading them all so we don't have to write them all out again when we quit.
Merge branch 'dynamic-submap-loading' of https://github.com/kevingranade/Cataclysm-DDA into kevingranade-dynamic-submap-loading

Conflicts:
	src/mod_manager.cpp

Fixes as BevapDin proposed.
Merge branch 'kevingranade-dynamic-submap-loading'