feat: create validator for IPv4 addresses

[rafamizes]

Closes #97

[codecov]

Codecov Report

Merging #149 (d997630) into master (3dc92b1) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #149   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           41        43    +2     
  Lines          397       409   +12     
=========================================
+ Hits           397       409   +12     

Impacted Files	Coverage Δ
lib/src/net/ipv4.dart	100.00% <100.00%> (ø)
lib/src/net/req_ipv4.dart	100.00% <100.00%> (ø)

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[rafamizes]

@rultor merge it.

[rultor]

@rultor merge it.

@rafamizes OK, I'll try to merge now. You can check the progress of the merge here

[rultor]

@rultor merge it.

@rafamizes Done! FYI, the full log is here (took me 2min)