Probe command (fix issue #33)

[pedrofaustino]

Here's a first take at adding the probe command. Please review and comment.

How can we use the MockServer to add tests?

[nramirezuy]

I don't get the use case of this command, can you illustrate me?

[srmaximiano]

See issue description on #33

[nramirezuy]

That url responds and not have the text searched, can be confusing.

[nramirezuy]

I think we need a way to get a set of headers per scrapy project.
I kind of dislike the headers hard coded on the class, can you add them to default_settings.py?

[nramirezuy]

@dangra Anything preventing this to be merged? Besides __future__.print_function

[kmike]

it should be 0.25 or 0.26, I'm not sure

[dangra]

0.26

[eLRuLL]

related issue #33 was closed as there isn't a necessity for this feature to leave inside scrapy and there is already a tool that can be used for the same functionality: minreq

Closing this PR.