feat: add CreateExitSpanWithContext

[kagaya85]

resolve #125

[codecov-commenter]

Codecov Report

Merging #126 (6a9dfde) into master (ddc26b2) will increase coverage by 0.25%.
The diff coverage is 69.23%.

@@            Coverage Diff             @@
##           master     #126      +/-   ##
==========================================
+ Coverage   69.33%   69.59%   +0.25%     
==========================================
  Files          17       17              
  Lines         887      888       +1     
==========================================
+ Hits          615      618       +3     
+ Misses        224      223       -1     
+ Partials       48       47       -1     

Impacted Files	Coverage Δ
trace.go	82.47% <69.23%> (+2.26%)	⬆️

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[rainbend]

LGTM

[wu-sheng]

Quick pull request, thanks.