feat: implement gnet on Windows

[panjf2000]

Fixes #339

[codecov]

Codecov Report

Patch coverage: 80.93% and project coverage change: +0.80 🎉

Comparison is base (2e95df1) 76.06% compared to head (93a1d6b) 76.86%.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #461      +/-   ##
==========================================
+ Coverage   76.06%   76.86%   +0.80%     
==========================================
  Files          15       21       +6     
  Lines        1508     2330     +822     
==========================================
+ Hits         1147     1791     +644     
- Misses        279      411     +132     
- Partials       82      128      +46     

Flag	Coverage Δ
unittests	76.86% <80.93%> (+0.80%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
acceptor_unix.go	42.37% <ø> (ø)
eventloop_unix.go	71.90% <ø> (ø)
listener_unix.go	100.00% <ø> (ø)
connection_unix.go	72.78% <50.00%> (ø)
connection_windows.go	64.52% <64.52%> (ø)
client_windows.go	79.45% <79.45%> (ø)
listener_windows.go	87.93% <87.93%> (ø)
reactor_default_bsd.go	87.32% <88.46%> (-3.16%)	⬇️
reactor_default_linux.go	83.14% <88.46%> (-2.04%)	⬇️
eventloop_windows.go	89.43% <89.43%> (ø)
... and 7 more

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