Features
* `TestCaseStdoutMixin` mixin to be used as multiple inheritance| along a TestCase class
* this mixin will provide the following assert methods to be used as a context
+ assertStdout(expected_output) will assert that the context will finish writing exactly expected_output in console
+ assertStdoutPrints(line1, line2, ...) is the same than assertStdout but passing each line
+ assertStdoutContains(expected_output) will assert that expected_output is a substring of the console output
+ assertStdoutRegex(regex) will assert that the console output matches with the provided regex