Review existing concepts

[IsaacG]

Give the concepts a review. Update as needed.

• arithmetic-operators
• basics
• booleans
• comments
• comparison
• conditionals-if
• conditionals-switch
• constants
• errors
• error-wrapping
• first-class-functions
• floating-point-numbers
• for-loops
• functions
• interfaces
• maps
• methods
• multiple-return-values
• numbers
• packages
• pointers
• randomness
• range-iteration
• regular-expressions
• runes
• slices
• stringers
• string-formatting
• strings
• strings-package
• structs
• time
• type-assertion
• type-conversion
• type-definitions
• variables
• variadic-functions
• zero-values