Add file type option which ignores file extensions other than provided

[mnojek]

Currently RFlint operates on .robot, .resource, .txt and .tsv file extensions but in RF 3.2 all extensions different than .robot and .resource. are not automatically supported (you need to provide them explicitly). There is also a file type .rst that RF supports but RFLint does not read it. By adding new command line option the user is able to select which file types will be processed and RFlint will ignore the others. The default supported files are .robot and .resource but you can also provide .txt, .tsv and .rst extensions.

The option is called by --filetypes or -t with extensions separated by comma, e.g. rflint -t robot,resource,txt

I added also test cases to cover this new feature.

[bhirsz]

Misaligned

[mnojek]

I did it on purpose, please look at the whole file. But I can revert it if it looks strange. What do you think?

[bhirsz]

Oh I see, thanks to this format it's easy to see that you're testing this or that file format combination. But maybe you could use this approach?

*** Test Cases ***    
Test Supported File Types    
[Template]      Run Rflint And Verify There Are No Errors For Supported File Types    
robot  resource  tsv    
robot  resource    
       resource    tsv    
robot              tsv    
robot    
      resource    
    

[mnojek]

Yeah, another approach is to use arguments embedded in keyword name. I will think which one is the best for this use.