First version of the IPTU Curitiba spider

* For now it takes just some fields of the carnet.
* The most important information is to know if the tested
registration number exist.
Minor change
Minor changes: documentation
The string cleaner pipeline is not necessary anymore

* The job is done inside the own Item class.
The range of IPTU values can be passed by command line
Readme update
Added nature field for IptuCuritiba