Implement a PARSERS setting

[Gallaecio]

Fixes #312, fixes #525

[codecov]

Codecov Report

Merging #603 into master will increase coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #603      +/-   ##
==========================================
+ Coverage   95.12%   95.21%   +0.08%     
==========================================
  Files         302      302              
  Lines        2504     2506       +2     
==========================================
+ Hits         2382     2386       +4     
+ Misses        122      120       -2

Impacted Files	Coverage Δ
dateparser/timezones.py	100% <ø> (ø)	⬆️
dateparser/parser.py	98.89% <ø> (+0.54%)	⬆️
dateparser/data/date_translation_data/en.py	100% <ø> (ø)	⬆️
dateparser/data/date_translation_data/nb.py	100% <ø> (ø)	⬆️
dateparser/utils/strptime.py	100% <ø> (ø)	⬆️
dateparser/freshness_date_parser.py	98.94% <100%> (ø)	⬆️
dateparser/languages/locale.py	98.65% <100%> (ø)	⬆️
dateparser/date.py	98% <100%> (+0.02%)	⬆️

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[noviluni]

I think it is a really good idea. Moreover, it is necessary to implement this in some way to allow showing what parser has been used when implementing the DEBUG_INFO flag (draft PR: https://github.com/scrapinghub/dateparser/pull/561/files)

[noviluni]

Really good job here.

Maybe it's not necessary to add it before merging, but it could be a good idea to mention the existing "parsers" in the docs explaining what each one does.

Related to this are the parsers names. I think we should meditate on the names as then are going to be a “public API”. Adding the explanation to the docs will help us to find out the best name for each parser.

[noviluni]

@Gallaecio

[Gallaecio]

Added the list of parsers to the documentation with a brief description about each one of them.

[noviluni]

I left some comments. Really good job here, it could be amazing to include this in the next release (expecting to be this month).

[noviluni]

Ok, I like the approach.

I would mention the "settings" in the error, to make easier to find and fix the error, but it's not necessary, it works as expected.