Add GetString function

[goodspark]

Resolves #53

Convenience function so users don't have to do:

s := string(v.GetStringBytes("key", "a", "b"))

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.01%. Comparing base (1649ca5) to head (da55489).
Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #54      +/-   ##
==========================================
+ Coverage   97.00%   97.01%   +0.01%     
==========================================
  Files           9        9              
  Lines        1067     1072       +5     
==========================================
+ Hits         1035     1040       +5     
  Misses         19       19              
  Partials       13       13              

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[goodspark]

I didn't add an equivalent String function because that would collide with the existing one that returns a string representation of the value.

[valyala]

Unfortunately this won't work as expected, since the returned string will contain garbage after the next call to Parser.Parse, since v.s is backed by byte slice, which is modified on each Parser.Parse call.

[goodspark]

What do you suggest?

[valyala]

Either stick to string(v.GetStringBytes()) or use something unsafe like toUnsafeString(v.GetStringBytes()) if you know possible consequences of improper usage of the returned unsafe string.

[goodspark]

What if GetString returned string(v.GetStringBytes())?

[phuslu]

string(v.GetStringBytes()) will do a memory copy.
I think add "GetString" is not a good idea, we shall keep GetStringBytes and let users choose use b2s() or string() in their usecases.