diskpart - simplify the help system

Changelog:
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• Simplified the help system
• Removed an unnecessary check in the help system that listed the first help entry 'active' no matter what was entered into the help system, even if the word is not in the list.
• Removed exit_main and rem_main functions since it took a little extra processing time and made the code a bit harder to read. Now it determines if the given command is rem or exit first before looking through the entire function list.
• Converted WCHAR* to LPWSTR to make it a bit easier to read.
• Add a title to the program to make it easier for the user to determine the name of the application currently running, especially if a large script is being used.