Add width parameter in col

[johnferchermeli]

Description

• Width parameter works like bootstrap
• Adapt all components to work with the new version
• Updates docs;

Related Issue
resolves #129

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/structs/interfaces has comments upside them explaining they responsibilities
• Executed go fmt github.com/johnfercher/maroto/... to format all files

[codecov-io]

Codecov Report

Merging #139 into master will increase coverage by 1.23%.
The diff coverage is 95.48%.

@@            Coverage Diff             @@
##           master     #139      +/-   ##
==========================================
+ Coverage   95.00%   96.22%   +1.23%     
==========================================
  Files           9        9              
  Lines         559      582      +23     
==========================================
+ Hits          531      560      +29     
+ Misses         22       16       -6     
  Partials        6        6              

Impacted Files	Coverage Δ
internal/tablelist.go	67.86% <63.64%> (+9.53%)	⬆️
internal/text.go	93.34% <95.00%> (-6.66%)	⬇️
internal/code.go	100.00% <100.00%> (ø)
internal/image.go	100.00% <100.00%> (ø)
internal/math.go	100.00% <100.00%> (ø)
internal/signature.go	100.00% <100.00%> (ø)
pkg/pdf/pdf.go	100.00% <100.00%> (+1.47%)	⬆️
pkg/props/prop.go	100.00% <100.00%> (ø)

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