Move Codebase to Golang

[martialblog]

We have discussed the future of the plugin internally and we have decided to move to Golang to improve maintainability and simplify usage.

Fixes: #18 #20

The functionality will be mostly the same.

Notable changes in functionality:

• Improve output strings, the output strings that are mapped from the returned SNMP bytes are now the same as in the vendor docs
• The mapping of the contact string was probably wrong, this was corrected according to the vendor docs
• Add support for SNMP v3 (is now the default method, but with noAuthNoPriv)

[martialblog]

Needs to be tested against more devices and the SNMP v3 needs to be tested as well.

[martialblog]

@log1-c Hi, I have compiled a Preview of the new version here, in case you want to help test it: https://transfer.netways.de/index.php/s/zL3EjBwTNBgKtPe

Feedback is very welcome

[log1-c]

As I am on holiday next week and the check runs on a customers monitoring system, I won't be able to give feedback quickly.
I will schedule a short appointment with the customer for the week after next :)