Add match_word option to git blacklist task

[morloderex]

Added a match_word option to git blacklist.

Closes: #803

Q	A
Branch	master for features and deprecations
Bug fix?	yes
New feature?	yes
BC breaks?	no
Deprecations?	no
Documented?	yes
Fixed tickets	#803

So I figured my issue #803 out by myself, as it turns out git grep command has an option called word --word-regexp or -w for sorthand.

This has been taken from the Git scm documentation

Match the pattern only at word boundary 

(either begin at the beginning of a line, or preceded by a non-word character; end at the end of a line or followed by a non-word character).

I have added the possiblity to opt-in to this functionallity by using the new match_word option on the task. However I am fully open to changing this option on the task to something else. Some alternative naming conventions considered strict_keywords, match_keywords, match_using_boundary

All tests passes however let me know if I need to address anything before this can be merged I am new to contributing here.

[veewee]

Thanks for the PR, it looks good!
I've added 2 small remarks.

[veewee]

Thanks for your work!