Example code for basic Call and Prepare/Flush.

Example functions for a simple Put & Get using Call(), and then for
Prepare() & Flush().

Each example is self-contained, and includes the server
setup/teardown.  This makes the code closer to what would be used in
an actual client program.

The Prepare() & Flush() is a bit long because we have to create the values
we are later scanning for.
This was based on the example code in client/docs.go, which I used as a starting point.  If it is not normally necessary to specify the isolation level, I'm glad to take it out.