Feature/upgrade go 1.15.6 (#5)

* upgrade go to 1.15.6

* add gcc-arm-linux-gnueabi, fix paths in sqlitetst

Co-authored-by: Stephan Hradek <[email protected]>

Refactor library API and provide more helpers. Support Go 1.9.

* Support for Go 1.9

* Refactor and rewrite most of API surface

* Merged SDK Dockerfile into repository

* Provide helpers for networking, certs and wrapper for CLI apps

* Add README