Update main.py

* changed  key names of the returned dict from the IOS and NXOS parser (dev_info). Now the key names follow proper naming convention. 
* changed the string formatting code on the generate_config() function to look cleaner. Now a single argument is passed to the .format() string method = the filled dictionary. 
* changed the interface_shortener funtion so collapse all of the 'if, else' statements that look at 'if remote_inf startswith X'  into a single rexeg lookup. The function then takes the matched object and uses a dictionary that has all of the mappings {'Ethernet': 'Eth', 'FastEthernet': 'Fa'}...etc. If no match object is found from the regex, the original remote_intf is returned.