fix(library/tactic/intros_tactic): seg fault at intros tactic, fixes #366
feat(frontends/lean): nicer notation for dependent if-then-else
feat(library/definitional): add "datastructure" for storing recursive equations
feat(library/definitional/equations): add support for serializing equations
feat(frontends/lean): parse "decreasing" expressions
chore(library/definitional/equations): fix style
refactor(frontends/lean/decl_cmds): cleanup definition_cmd
feat(frontends/lean): parse recursive equations
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