Added functionality for high and low tax types

[SebastiaanKloos]

In the Netherlands we have more than one tax rate.

High: 21% and Low: 6%.

https://www.belastingdienst.nl/wps/wcm/connect/bldcontentnl/belastingdienst/zakelijk/internationaal/btw_voor_buitenlandse_ondernemers/btw_berekenen/btw_tarieven/

I've added this functionality to this repository to help Dutch users.

[mpociot]

Thank you! Can you add a test for this too?

[codecov-io]

Codecov Report

Merging #49 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #49      +/-   ##
==========================================
+ Coverage   94.66%   94.71%   +0.05%     
==========================================
  Files           5        5              
  Lines         206      208       +2     
==========================================
+ Hits          195      197       +2     
  Misses         11       11

Impacted Files	Coverage Δ
src/Mpociot/VatCalculator/VatCalculator.php	93.23% <100%> (+0.1%)	⬆️

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[SebastiaanKloos]

@mpociot I'll try to add a test to it!

[SebastiaanKloos]

I've added some tests. @mpociot

[SebastiaanKloos]

@mpociot Can you please review my code and merge if accepted?

[mxmtsk]

I was just about to open an issue for this. Any updates on when this will be merged? Germany also has two tax types, 19% and 7%

[SebastiaanKloos]

@mxmtsk no response yet from moderators

[mxmtsk]

@mpociot Any thoughts on this, it's been a while? :)
@SebastiaanKloos would you consider adding another checkin to make it more complete and reflect Germany also?

            'rate'   => 0.19,
            'rates' => [
                'high' => 0.19,
                'low' => 0.07,
            ],