code opt: performance optimization

[hcraM41]

1.file: client.go function: urlencode
a Builder is used to efficiently build a string using Write methods. it minimizes memory copying. Builder directly converts the underlying []byte to a string type and returns it.
BenchmarkURLEncodeBuilder-8 5000000 220 ns/op 64 B/op 2 allocs/op
BenchmarkURLEncodeBuffer-8 4000000 280 ns/op 80 B/op 3 allocs/op

2.file: client.go function: urlencode
reduce memory allocation: avoid the redundant operation of extracting the last "&" at the end.

3.file: server_reflection.go function1:String function2:GetServices
replace bytes.Buffer with strings.Builder.