perf: use strings.Builder in GoString

[zedongh]

for large json validation may cause mess validation error, string concat cause poor performance, use byte.Buffer much better

[santhosh-tekuri]

please make following changes:

• use strings.Builder for better performance; see here
• change commit msg to perf: use strings.Builder in GoString
• rename writeIntoBuffer to goStringTo
• rename msgBuf to tgt
• move new method to after GoString method
• use loop to print indent; using strings.Repeat creates heap alloc which immediately discarded
• replace WriteRune('\n') with WriteByte('\n')

[santhosh-tekuri]

also ensure gofmt and govet is done on file;

[zedongh]

please make following changes:

• use strings.Builder for better performance; see here
• change commit msg to perf: use strings.Builder in GoString
• rename writeIntoBuffer to goStringTo
• rename msgBuf to tgt
• move new method to after GoString method
• use loop to print indent; using strings.Repeat creates heap alloc which immediately discarded
• replace WriteRune('\n') with WriteByte('\n')

done

[zedongh]

also ensure gofmt and govet is done on file;

done