Add chapter_55: Errors
Add chapter_56: Exercise: Errors
Modify to output error
Add type and function
Add chapter_57: Web servers
Add chater_58: Exercise: HTTP Handlers
Add chapter_59: Images
Add chapter_60: Exercise: Images
Add chapter_61: Exercise: Rot13 Reader
Add chapter_63: Goroutines
Add chapter_64: Channels
Add chapter_65: Buffered Channels