Added UserIO Implementation to main file

- Added userIO implementation to main project
- Changed push/pull to output/input
- Documented
- Removed Add and Delete print functions (Unneccesary)
- Added Input char* length constants
- Split Prompt() to StringPrompt() and MenuPrompt()
- Added str2Int function for menu parsing
- Changed Push::Item(ListItem* item) to Output::PrintItem(ListItem&
item)
- Miscellaneous function name changes.