Updated versions and Go code
Version changes
- Upgrade Alpine to 3.12
- Upgrade Go to 1.15
- Using cod4x 18.0's pre-built files (xbase_00.iwd for alpine, steam and cod4x binaries for debian)
Code details
- Upgrade golibs dependency
- Rework HTTP server code
Development tooling
- Update devcontainer definition
- Upgrade golangci-lint to 1.33.0 and add all linters
- Improve Github workflows