Add chapter_16: Numeric constants
Add chapter_17: For
Add chapter_18: For continued
Add chapter_19: For is Go's "while"
Add chapter_20: Forever
Add chaper_21: If
Add chapter_22: If with a short statement
Add chapter_23: If and else
Add chapter_25: Structs
Add chapter_26: Struct Fields
Add chapter_27: Pointers
Add chapter_28: Struct Literals