feat(util/rb_tree): add max (element) method

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean/info_manager): several bugs: invalid flag was not being reset for empty lines, merge with overwrite=false was adding 'poluting' state, --NAY generation

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(emacs/eri.el): add eri.el (from agda mode)
feat(emacs/lean-mode): add lean-tab-indent-or-complete

Close #105
feat(bin/linja): add tags target

fix #117
feat(emacs/lean-tags): call "linja TAGS" to make TAGS

fix #117
fix(bin/linja): use ninja binaries at leanprover.github.io

fix #118
chore(emacs/lean-mode): add package info
feat(emacs/lean-option): provide candidates and validation for lean-set-option

Close #106
fix(frontends/lean/info_manager): user provided options override saved options, fixes #119

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/data/subtype): elaborator does not need help anymore (i.e., 'show'-expression) for this file

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/data/list): avoid placeholders '_', make first argument of false_elim implicit

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(emacs/lean-cmd): add lean-clear-cache

Close #99
feat(bin/linja): add clear-cache target

Close #99
checkpoint for imenu