feat(isCPF): adding validator for CPF (brazilian SSN)

[renanmontebelo]

Adding validator isCPF(str, options). CPF in Brazil is analogous to Social Security Number in the US.

The validator has options to require, disallow or don't care (default) about separator characters.

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)

[codecov]

Codecov Report

Merging #1589 (be193cb) into master (1b85829) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1589   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          100       101    +1     
  Lines         1796      1820   +24     
=========================================
+ Hits          1796      1820   +24     

Impacted Files	Coverage Δ
src/lib/isPassportNumber.js	100.00% <ø> (ø)
src/index.js	100.00% <100.00%> (ø)
src/lib/isCPF.js	100.00% <100.00%> (ø)
src/lib/isDataURI.js	100.00% <100.00%> (ø)
src/lib/isIdentityCard.js	100.00% <100.00%> (ø)
src/lib/isMACAddress.js	100.00% <100.00%> (ø)
src/lib/isStrongPassword.js	100.00% <100.00%> (ø)

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[tux-tn]

I closed the PR to rerun the tests. Thank you for your contrib @renanmontebelo , can you please explain the difference between isCPF and the existing isTaxID ?

[renanmontebelo]

Closing in favor of #1613

[renanmontebelo]

@tux-tn now that I know better, isCPF should indeed be part of isTaxID. #1613 uses this approach so I'm closing this PR in favor of that one. Thank you!