[Patch] Add name to "no breaking space" character

Hi, when trying to load spinneret <https://github.com/ruricolist/spinneret> on ABCL it would fail as ABCL does not recognize the character #\No-break_space <https://github.com/ruricolist/spinneret/blob/master/syntax.lisp#L37>. The character in question is named #\_. This patch adds a human readable name, #\No-break_space, which is used in sbcl, ccl and clisp, and permits spinneret to load. Hope it is adequately formatted as I'm not familiar with svn, Javier Olaechea -- "I object to doing things that computers can do." — Olin Shivers