Look into binary encoding for certain data types

[sfackler]

At least for primitive numeric types and byte arrays, this should help avoid a lot of allocations.

[sfackler]

REAL and DOUBLE PRECISION values are interesting here. On one hand, we want to send them in binary formats since lossless conversion between floating point numbers and strings is notoriously hard and most implementations are subtly broken. On the other hand, it appears that Postgres does not guarantee that its floats are IEEE754 internally. It's unclear if non-IEEE754 platforms translate to and from IEEE754 when sending over the network. Integral types are sent big-endian, so the binary format is slightly abstracted from the underlying implementation. It's also unclear if there are any non-IEEE754 platforms that anyone actually wants to run a Postgres server on.

[sfackler]

Handling binary data in FromSql will be more complicated than ToSql since we have to specify if we want binary or text data at Bind time. If we decide in #14 to be extremely strict matching types, this is fine since we can ask for binary data for all of the types the driver knows about at least. Unknown types may be forced to use the text format or we could support some system to register binary types with a connection for programs that have implementations of FromSql for things like PostGIS types.