Feature/labstack echo contrib

[rv-rsouza]

Labstack Echo light web framework middleware implementation.

Closes #174

[gbbr]

Wow! You're fast. I was hoping to discuss it a bit within the issue before starting the work. Then I would've gotten a chance to tell you that we are not adding any more features to this version of the tracer (meaning the master branch).

We are now working on v1 which is soon to be released, so we will have to add these changes there. I can see you got inspired from other integrations when writing the code, which is great! You can do so by looking at the gin-gonic/gin integration for inspiration on the v1 branch, and at gorilla/mux for inspiration on tests (we want table tests).

Thanks for putting in the work and I'm sorry you had to write this. I really was hoping to get a chance to talk about it before committing to work.

[rv-rsouza]

Ops!

I've found some time to do it yesterday. Maybe I can find some time to change to the new structure this week.

Thank you for the great tool you maintain. I was just giving a little contribution to your work.

[gbbr]

Thanks for understanding. And I'm glad you like our tracer! I'd advise you to start clean instead of changing this code. Looking forward to your contribution!