Fixes #457, refactor sengrid get method of Mail class

[Prashant-Surya]

Refactored Mail class in sendgrid/helpers/mail which would fix get method complexity.

[SendGridDX]

All committers have signed the CLA.

[codecov-io]

Codecov Report

Merging #486 into master will decrease coverage by 5.15%.
The diff coverage is 84.61%.

@@            Coverage Diff             @@
##           master     #486      +/-   ##
==========================================
- Coverage   87.91%   82.76%   -5.16%     
==========================================
  Files          30       30              
  Lines         935     1021      +86     
  Branches      115      158      +43     
==========================================
+ Hits          822      845      +23     
- Misses         55       86      +31     
- Partials       58       90      +32

Impacted Files	Coverage Δ
sendgrid/helpers/mail/mail.py	96.2% <84.61%> (+1.43%)	⬆️
sendgrid/helpers/inbound/send.py	0% <0%> (-93.75%)	⬇️
sendgrid/helpers/mail/category.py	81.81% <0%> (-18.19%)	⬇️
sendgrid/helpers/mail/asm.py	73.91% <0%> (-10.09%)	⬇️
sendgrid/helpers/mail/section.py	85.71% <0%> (-8.41%)	⬇️
sendgrid/helpers/mail/header.py	85.71% <0%> (-8.41%)	⬇️
sendgrid/helpers/mail/substitution.py	85.71% <0%> (-8.41%)	⬇️
sendgrid/helpers/mail/custom_arg.py	85.71% <0%> (-8.41%)	⬇️
sendgrid/helpers/mail/ganalytics.py	79.66% <0%> (-7.58%)	⬇️
sendgrid/helpers/mail/subscription_tracking.py	80.48% <0%> (-7.4%)	⬇️
... and 19 more

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[thinkingserious]

@Prashant-Surya

We have not been able to merge your Pull Request, but because you are awesome - we wanted to make sure you could still get a SendGrid Hacktoberfest shirt.

Please go fill out our swag form before Nov 5th and we will send the shirt! (We know that you might have tried this before and it didn’t work, sorry about that!)

You have till Nov 5th to fill out this form in order to get the Hacktoberfest shirt!

Thank you for contributing during Hacktoberfest! We hope to see you in the repos soon! Just so you know, we always give away a SendGrid shirt for your first ever non-Hacktoberfest PR that gets merged.

[Prashant-Surya]

@thinkingserious Thank you :) I will contribute more to sendgrid repos.

[thinkingserious]

That’s awesome @Prashant-Surya, thank you!

[thinkingserious]

Thanks again for helping improve this SDK!

We have started to execute on PR #347 (Python Mail Helper Refactor) and have integrated your work into this branch. Please follow along at PR #347 to follow our progress.

With Best Regards,

Elmer