feat(emacs/lean-company): truncate string if it's longer than 90% of window-width

Also add "..." in the end

Close #137
feat(library/data/empty): add false.to_empty and false.rec_type theorems

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/data/category): add category theory

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/data/category): add vector

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(emacs/lean-server): scroll debug buffer
feat(emacs/README.md): add instruction for unicode font
feat(emacs/lean-server): add debug-mode, trace-mode
refactor(emacs/lean-server): restructure async queue handling routine
feat(emacs/lean-flycheck): delete flycheck temporaries after check

Close #140
feat(bin/linja): --flycheck option takes a width argument

Close #28
feat(emacs/lean-settings): pass 'pp.width' to lean via linja

Close #28
feat(util): add fuzzy string search procedure
feat(frontends/lean/server): using fuzzy matching
feat(frontends/lean/server): sort fuzzy matches by number of errors

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