config: Refactoring. See description.

- Moved Map type and SortedMap to config/map.go.
- Don't use log.Fatalf in ParseFile method, return error.
- Added Save(file string) method.
proto/packet: Refactor chunk packets 0x33 & 0x38.

Both:
- Renamed field GroundUpContinuous -> AllColSections.
MapChunkBulk
- Deleted Count and Length fields in favor of slices len builtin
function.
bin/minero: Add default config.
server: Add default config generator.