Add parameter command line option

[wdahlenburg]

Added the -p or --parameter option as a way to specify which parameter to attempt template injections on. By default all parameters are still tried.

For the example in the Readme:
python ./tplmap.py -u "http://127.0.0.1:8000/page?name=John&foobar=test" -p name

Only the name parameter will be tested.

This can be useful for reducing the number of attempts required to exploit and provides an alternate syntax to injecting the '*' character.

[shelld3v]

Hey @wdahlenburg, I have already done this in my PR: #79. Just the fact that @epinna didn't merge it

[wdahlenburg]

Dang this could have saved me some time yesterday. It looks like we both chose different places in the code to filter for specific parameters.

I'll leave preference up to @epinna

[shelld3v]

🙄