fix(frontends/lean/parser.cpp): fix typo
feat: add "--flycheck" option to print out error msgs for flycheck
fix(kernel/converter): missing constraints

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(library/unifier): process_flex_rigid method before adding yet another case split

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>