[perl6/specs] db9924: [S15] Change .chr(s) to return Uni, not Str.

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/perl6/specs
  Commit: db9924434cfbf1d13fd79c461ace06ebc90b348d
      
https://github.com/perl6/specs/commit/db9924434cfbf1d13fd79c461ace06ebc90b348d
  Author: lue <rnd...@gmail.com>
  Date:   2013-12-13 (Fri, 13 Dec 2013)

  Changed paths:
    M S15-unicode.pod

  Log Message:
  -----------
  [S15] Change .chr(s) to return Uni, not Str.

This is because Uni is the only string type that won't convert strings
given to it, which for people who are playing with numeric arrays of
codepoints is probably important.