Removed custum usage message on parse error

When the user sends wrong command line arguments the default behavior from
`argparse` python standard module is executed.
Removed the duplicated code for parsing the configuration file

At several places in the code logic is implemented to read the configuration.

The solution is to remove this duplication by pooling the business logic into
a single function (eg `parse_rc`).

Finally it will be better to read the configuration only once.
Improved the steps clarity into the main

Steps on the main are a little unclear.

So adding some comments to explain what's happening.

In the future it should be better to avoid writing a lot of code in it.