Towards Avatica-Go 5.1.0

[Francis Chuang]

Hey everyone,

It's been quite a while since the last Avatica-Go release, more than 2 
years!

I have been doing some housekeeping and upgrading dependencies, etc. I 
think it's probably a good time to release 5.1.0.

I believe I have completed most of the housekeeping. I plan to make rc0 
available for voting in the next few days or early next week, time 
permitting.

Francis