Create prepared statement examples

[ToddGreenstein]

Simon has started on this for Java, we will follow the example for all of the sdk's

[simonbasle]

pinging @couchbaselabs/sdk-team so that people follow this 👀

[mnunberg]

While I support this in theory, I don't know if we shouldn't just merge the 'prepared statement' example in the normal query placeholder example, or place the prepared stuff in comments, like so:

q = N1QLQuery(...)
# Uncomment the next line to make this a 'prepared' query
# q.adhoc = False

Rather than repeating an almost identical example just for one single flag. Since there is absolutely no user-facing different (other than a simple flag, and hopefully increased performance..)

[simonbasle]

ah didn't see Mark's remarks 😦, maybe I should have done a pull-request