Add [Not]Contains assertions & corresponding [Not]Found failures.

[matthieu-vergne]

Here I add the assertContains asked in #59.
It is quite different from #96:

• I go further in terms of renaming, with proper container and content names ;
• Parameters are container first, content second, while Add assertContains function - #59 #96 is the reverse ;
• I don't use od because I am not familiar with it and multi-line was not part of my use cases. Maybe good to add ;
• I also add assertNotContains for the symetry ;
• I also add failFound and failNotFound ;

[kward]

Thank you for the pull!

[matthieu-vergne]

Thank you for accepting it. {^_^}