This change simply copies over the private Go profiler into the
`profiler` package of `dd-trace-go`.

This change removes the option of adding a custom logger and instead
uses the already existing logger from dd-trace-go which will prefix
messages with `Datadog Tracer %version%: %message%`

This change temporarily removes environment variables until we decide
for a standardized naming.

This change adds `WithService` to the tracer as an alias for
`WithServiceName` which now becomes marked as deprecated. It also
renames `WithServiceName` to `WithService` in the `profiler` package.

Additionally, these are added to the example, along with the version
tag.