fix(emacs/lean-server): limit the number of NAY retries

Also, only retry when there is no continuation other than the current
one.
fix(emacs/lean-company): override company--window-width

Override 'company--window-width' to be 0.95 * window-body-width.
This partially solves the problem of issue #137.
refactor(emacs/lean-flycheck): clean up unused code
chore(emacs): minor adjustments to synthax hightlight and input mode

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
doc(server): add FINDG and FINDP documentation, closes #144

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