Added `USERPROFILE` environment variable for Windows

The `HOME` environment variable on Windows is call `USERPROFILE`.
Merge pull request #34 from alquerci/add/homepath_lookup

Added USERPROFILE environment variable for Windows for config path lookup
Moved user config file detection to a dedicated method
Use the program usage of the argparse Python module on a parse error
Moved the `CygAptSetup` instantiation after argv parsing
`parse_rc` now parse all configuration
Clarified the steps on `CygAptMain.main` method