Add custom page margins

[happsie]

Description

• Added a new method on the Maroto PDF interface to allow backwards
  compatibility instead of adding extra parameter to NewMaroto

This PR makes it possible to set other margins than the standard (10, 10, 10)

Picture of sample1 modified with SetPageMargins. 30 left, 20 top and 0 right.
m.SetPageMargins(30, 20, 0)

Related Issue
resolve #123

Checklist

check with "x", if applied to your change

• All methods associated with structs has func (s *struct) method() {} name style.
• Wrote unit tests for new/changed features.
• Updated docs/doc.go
• Updated pkg/pdf/example_test.go
• Updated README.md
• Updated all examples inside internal/examples
• New public methods has comments upside them explaining what it does
• Executed go fmt github.com/johnfercher/maroto/... to format all files

[codecov-io]

Codecov Report

Merging #122 into dev will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev     #122      +/-   ##
==========================================
+ Coverage   95.22%   95.25%   +0.04%     
==========================================
  Files           9        9              
  Lines         522      526       +4     
==========================================
+ Hits          497      501       +4     
  Misses         21       21              
  Partials        4        4

Impacted Files	Coverage Δ
pkg/pdf/pdf.go	100% <100%> (ø)	⬆️
internal/signature.go	100% <100%> (ø)	⬆️

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[johnfercher]

I think your feature is nice. I let some comments, could you see it?

Just one more thing, could you provide in your pull request a print screen of the effect of your modification? Maybe just run the sample1 and see if everything works properly with your modificati0on.

https://github.com/johnfercher/maroto/tree/master/internal/examples/sample1

[johnfercher]

Looks like the signature component doesn´t work well with this, I will take a look in this issue before merge your PR.

[happsie]

Update PR with improvements from comments.

[johnfercher]

Have a look to https://github.com/Jepzter/maroto/pull/1/files, I fixed the issue in the signatures

[johnferchermeli]

Could you merge my PR into your branch? So I will be able to merge your branch into dev.

[johnferchermeli]

Niice, could you update the sample image with the fix?

[happsie]

Sorry for being late, updated PR with image.

[johnferchermeli]

Hey, happy new year =) I will merge this PR today.

[happsie]

Happy new year to you to! Is there any reason this is still open I can fix?

It's me