Adhere to standard GNAT file naming rules

http://gcc.gnu.org/onlinedocs/gnat_ugn_unw/File-Naming-Rules.html

1. Files changed to lowercase
	Without the change the gnat compiler emitted the following warning:
	Main.adb:26:11: warning: file name does not match unit name, should be "main.adb"

2. Missing file extension on one file
	Windows/Neo-System-Implementation_For_Operating_System