Pysaga-cmd

Fixed the parameter names inside the **get_tool** method.

- Added an **Output** class and plotting functions;
- Classes are now defined with the **attrs** library.

- The 'tool_idx' parameter when constructing a Tool class has been changed to 'tool' and now takes a string as input.
- The 'library_name' parameter when constructing a Library class has been changed to 'library'.
- The 'library_name' attribute of a Library object has been changed to 'name'.
- The shell=True argument of the run_command() method has been removed.

Added a shell=True argument to SAGA.run_command().

First functional release.