Integrates the check-doc.py script to arcanist

Summary:
Running arc lint or arc diff will run the script.
An error will be returned for each undocumented or unknown argument.

Depends on D2306

Test Plan:

arc lint

Check there is no error

Add this line to src/init.cpp (don't forget to save):

// GetArg("-dummy", "default");
arc lint

Check it outputs an undocumented argument error for -dummy
Remove the line from src/init.cpp

Add this line to src/init.cpp (don't forget to save):

// HelpMessageOpt("-dummy", "Dummy documentation");
arc lint

Check it outputs an unknown argument error for -dummy
Remove the line from src/init.cpp

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2307