add request to dial callback

[kotori2]

Close #44

[kotori2]

> go test ./...
ok      github.com/things-go/go-socks5  (cached)
ok      github.com/things-go/go-socks5/bufferpool       5.189s
ok      github.com/things-go/go-socks5/statute  2.811s

[thinkgos]

@kotori2 Non-compatible change, suggest add another dial(Such as CustomDial) to overiwrite default dial, which priority higher than dial

[kotori2]

@kotori2 Non-compatible change, suggest add another dial(Such as CustomDial) to overiwrite default dial, which priority higher than dial

Yeah that's what I'm thinking about in the first place...
Gonna make this PR as draft first.

[kotori2]

done

> go test ./...                
ok      github.com/things-go/go-socks5  1.378s
ok      github.com/things-go/go-socks5/bufferpool       4.424s
ok      github.com/things-go/go-socks5/statute  0.285s

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6191a34) 62.19% compared to head (5438f4d) 63.13%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #45      +/-   ##
==========================================
+ Coverage   62.19%   63.13%   +0.94%     
==========================================
  Files          14       14              
  Lines         775      784       +9     
==========================================
+ Hits          482      495      +13     
+ Misses        233      230       -3     
+ Partials       60       59       -1     

Flag	Coverage Δ
unittests	63.13% <100.00%> (+0.94%)	⬆️

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[kotori2]

Do I need to add test cases for the options?