Print line violations only under --verbose flag

[ulysses4ever]

Alleviates #48 but a proper performance fix would be better. Also, --verbose already existed, so I reused it. Maybe, it's a bad idea, 'cause it will be impossible to find anything in a string of [ Checked ] (this is what --verbose currently means: it prints this for all non-violating files). But that's what was suggested in #48… Opinions?

Otherwise, I put back the old implementation beside the new one, mostly. Some common bits are factors out.

Time measurements

v0.0.11 release
❯ time $FW --check 20000-violations.txt 2> /dev/null
Executed in   36.48 millis
❯ time $FW --check 200000-violations.txt 2> /dev/null
Executed in  100.67 millis

master:
❯ time $FW --check 20000-violations.txt 2> /dev/null
Executed in  661.54 millis
❯ time $FW --check 200000-violations.txt 2> /dev/null
Executed in    6.13 secs

patch
❯ time $FW --check 20000-violations.txt 2> /dev/null
Executed in   35.82 millis
❯ time $FW --check 200000-violations.txt 2> /dev/null
Executed in  123.55 millis
❯ time $FW --check -v 20000-violations.txt 2> /dev/null
Executed in  718.26 millis
❯ time $FW --check -v 200000-violations.txt 2> /dev/null
Executed in    6.42 secs

[ulysses4ever]

Actually, I probably don't need a new constructor: it only adds noise.

[ulysses4ever]

Done.

[ulysses4ever]

Hey @andreasabel! Do you think you could get back to this at some point? I totally understand if you have another priorities, of course.

[ulysses4ever]

Ping.

[andreasabel]

Thanks, I am trying to release this now.