Begin notes for chapter 13
Add notes from chapter 12
minigrep: Print errors to stderr
minigrep: Use case insensitive search depending on env
minigrep: Implement case insensitive search
minigrep: Add test for case insensitive search
minigrep: Make use of the search function
minigrep: Implement search function
minigrep: Add test for search function
minigrep: Remove obsolete printlns
Add notes for minigrep
minigrep: Split program into main and lib

Remember to make all the things public in lib.rs
minigrep: Handle result that run() returns
minigrep: Make run() return a result
minigrep: Move logic to separate function
minigrep: Make error output more user friendly
minigrep: Check number of args before parsing
minigrep: Make function a method of Config
minigrep: Use config struct instead of tuple
minigrep: Put argument parsing in separate function