Update to SDK v3

[autopulated]

Opening PR as requested #31 (comment)

Issues that need resolving still:

• the -sdkv3 suffix from the fork needs removing
• what to do about version numbers (keep on v4, or change?)
• behaviour of getParameter for a nonexistent parameter name needs to be resolved

[neo-peter-spangler]

please

[autopulated]

I've tested getParameter against a nonexistent parameter in aws, and both the sdk-v2 and the sdk-v3 versions throw a "ParameterNotFound" error, so I don't think that should block merging this. The identity of the thrown error type is obviously different, and it has different details, and that might justify releasing this as a new major version.

(The plural getParameters version also returns a response with both .Parameters and .InvalidParameters in both cases).