files.cpp:
- Refactored the way the file list works. Because we need to build & recurse a list up front, there will be possibly a ton of walking. So it now has a meta struct that stores head, tail, and size.
- Added zeroing out of initial data of file object
- Added timestamp to file object, stores value on creation
- Added routines to get file size of file list (in bytes) and walk a directory path & populate full list (not complete)

parcel.cpp:
- Began to move over to building full file list before starting any sending
- Added cleanup routine

receiver.cpp:
- Added cleanup routine
- Renamed global_data instance for clarification

sender.cpp:
- Added functionality for sender to handle postmaster messages
- Added preliminary functionality to send file list to reciever
- Added init/cleanup routines
- Refactoring handle_files to a) check if the file should be sent based on timestamp, and b) not recursively build file list