This change updates the doc.go documentation file with the correct use
of the new (since 8eead5217d) API used
for passing additional options when creating new script engines.
Spotted by davec@
This commit modifies the code to no longer require a protocol version. It
does this by making use of the new Serialize function in btcwire.
Unfortuantely this does entail a public API change which I generally don't
like to do, but eliminating the usage of the protocol version throughout
the codebase was important enough to warrant the change.