Instrumenting sqlalchemy

[codeboten]

Porting the existing sqlalchemy instrumentation to using the OpenTelemetry API and the OpenTelemetry Auto-instrumentation Patcher interface.

The process to make this happen is pretty straight forward:

1. move the redis code into the instrumentors directory
2. move tests
3. added setup/version files and move code into a similar directory structure to other opentelemetry integrations
4. fixed relative import paths to using ddtrace package
5. update the code to use opentelemetry API
6. get tests running

Couple of TODOs left:

1. add to travis
2. the original sqlalchemy instrumentation set a couple of metrics in the metadata, this could be a good opportunity to use the metrics API
3. figure out if Pin is needed

NOTE: This currently still uses some utility functions in the ddtrace package.

fixes #13

[codeboten]

closing in favour of open-telemetry/opentelemetry-python#591