Replaced use of custom buffer type with stdlib implementation

[balasanjay]

No description provided.

[balasanjay]

@julienschmidt, please take a look at this change when you get the chance.

I have an incoming pull request that lowers the number of allocations that is much nicer when the buffer used implements io.Reader.

[julienschmidt]

The driver originally used the bytes.Buffer but was replaced with the custom buffer for performance improvements in ccad956.
But I'm open to undo this if the performance losses are negligible when reusing the buffer. I'm testing and benchmarking now.

[julienschmidt]

Unfortunately, I notice performance degradation of ~ 8-9% (avg.) in Go 1.1beta2 and ~10% in Go 1.0.3.
You can play around with SQL-Benchmark if you want to try to optimize this.
I like the idea of this change, but from my point of view the current performance degradation is too large.

[julienschmidt]

Sorry i meant the #52 change.
I'm not going to merge this change here on its own so I'm closing this. Please continue the discussion at #52