feat(emacs): use lean-mode for .hlean
feat(*): add support for separate HoTT library
feat(build): add HoTT library to build
fix(build): clean-olean target should also clean HoTT library
feat(hott/init): add initialization files
fix(frontends/lean/parser): generate error when 'exit' command is used

m_theorem_queue.join() method assumes there are no open namespaces/scopes
fix(shell): use --server for .hlean files
fix(ltags): support .hlean files
feat(hott/init): add well-founded recursion to HoTT library
feat(hott/init/prod): show lex is well-founded in HoTT
feat(hott/init): add wf and prod to HoTT initialization
feat(emacs): add Type0 highlight
fix(util/lean_path): typo
feat(library/hott): port Floris' category implementation
feat(library/hott): try to replace the proof irrelevance
fix(library/hott): finish associativity proof
feat(library/hott): finish porting of natural_transformation.lean
feat(library/hott): port a part of algebra/category/constructions.lean, slice category still to do
feat(library/hott): add iso_of_path lemma for precategories
chore(library/hott): move precategory definition to its own folder