add args sample, changed generate_dartanalyzyer_list

[damondouglas]

Hello Everyone,

Instead of pushing directly, I am doing push request because changes are significant. Does anyone have any concerns? Thank you for letting me contribute.

Changes:

• Added example using args library.
• Added _tools/generate_dartanalyzer_list.dart script to enable dartanalyzer within each directory.

Here is the build success form my repository using drone.io: https://drone.io/github.com/damondouglas/dart-libraries-samples/2

[claudiodangelis]

Thanks!

[giolaq]

Awesome, let's continue this useful samples :)

[damondouglas]

Thank you for letting me be the honorary Italian.