feat(library/defitional): add no_confusion_type construction for inductive datatypes that are not propositions
feat(library/hott/trunc): prove that n-types are (n+1)-types.
feat(hott/trunc): clean up some theorems, prove some basic theorems
refactor(typeof): move typeof to general_notation
doc(algebra): update markdown files
style(library): rename set_category to discrete_category
style(library): some minor changes
feat(empty): define negation of types
feat(library): port truncation library from Coq HoTT

also made some minor changes in hott.equiv