Remove a solution.
Revert "Remove a solution."

This reverts commit e00d3e0eb133d052e6a3fb293065d2811249bc26.
New folder structure.
Exclude ".rkt~".
New tasks.
A lot of improvements.
Minor improvements.
One more example.
Housekeeping.
Ignore PLT Racket junk.
Merge branch 'master' into exercise-11

Conflicts:
	.gitignore
Merge branch 'master' into extra-02
Merge branch 'exercise-11' into extra-02