Add a print sanity function

[vkarak]

It would be quite useful for debugging sanity expressions to have deferrable version of print that would print its arguments and then return them, so that you insert it anywhere in a sanity expression:

self.sanity_patterns = sn.assert_eq(sn.count(sn.extract_all(...)), 10)

# print the extracted elements
self.sanity_patterns = sn.assert_eq(sn.count(sn.print(sn.extract_all(...))), 10)

[vkarak]

I have this ready, I am just waiting for #1050 to be merged. @teojgo Can you approve and merge it?

[teojgo]

@vkarak I merged it.