fix(basics.org): clarify input mode for web interface, closes #4
fix(basics): use simpler 'cases_on' recursor in "non-recursive" examples, and explain the idea behind it, closes #3
feat(basics): add "proof by reflexivity" section
fix(basics): missing definitions in the last example
feat(basics): add "proof by substitution" section
feat(basics): add "proof by case analysis" section
fix(basics): add extra space
feat(structures): add structure tutorial skeleton
feat(structures): add tutorial for structure command
feat(structures): use num instead of nat