Documentation: avoid stray backslashes in core tutorial

Documentation: avoid stray backslashes in core tutorial

While at it:

 - remove some single-quotes that were being rendered as ’\n\';

 - do not escape ellipses (...) when they do not represent the
   literal three characters "...".  We may want to ensure the
   manpages render these as three ASCII periods to make the
   manual pages easier to search, but that would be a global
   output generation setting, not a context-specific thing;

Reported-by: Frédéric Brière <fbriere@fbriere.net>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>