add only_replacements

[Jerry2001Qu]

Add option to only perform replacements. Useful for cleaning OCR output, as most mistakes are replacements.

[filyp]

Code looks great, good job! Please also add some short unit test in test_all.py and a short section in README, maybe # OCR to document the feature.

[filyp]

Benchmarks

Output of python test_all.py quality ; python test_all.py benchmark

before changes:

quality:
en  bad: 115/400
pl  bad: 23/40
tr  bad: 10/27
ru  bad: 1/10
uk  bad: 6/12
es  bad: 6/18
pt  bad: 7/13
cs  bad: 44/170

benchmarks:
english sentences        0.179s    bad: 0/3
english sentences fast   0.001s    bad: 1/3
spanish words            0.692s    bad: 6/18

after changes:

quality:
en  bad: 115/400
pl  bad: 23/40
tr  bad: 10/27
ru  bad: 1/10
uk  bad: 6/12
es  bad: 6/18
pt  bad: 7/13
cs  bad: 44/170

benchmarks:
english sentences        0.179s    bad: 0/3
english sentences fast   0.001s    bad: 1/3
spanish words            0.708s    bad: 6/18

so nothing got broken :)

[Jerry2001Qu]

Awesome, I've added a section in the README, and a unit test.

[filyp]

Great, thanks for contributing!