add: use advise function to display hints

add: use advise function to display hints

Use the advise function in advice.c to display hints to the users, as
it provides a neat and a standard format for hint messages, i.e: the
text is colored in yellow and the line starts by the word "hint:".

Also this will enable us to control the messages using advice.*
configuration variables.

Signed-off-by: Heba Waly <heba.waly@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>