Improve Perf by using bytes

[pyrossh]

Its seems the graphql-go guys tested their library for performance and improved it by a factor of 30 by using bytes instead of string. So I checked the source and even we are using string which causes a lot of garbage collection it seems so I guess we also need to make the change later to seem how much perf we gain.

References:
graphql-go/graphql@065ab6b
graphql-go/graphql#119

We should take a look at this lib for improving the lexer,
https://github.com/tdewolff/buffer