Modify read and print of combining characters

Modify read and print of combining characters

Since combining characters, such as accents, modify the appearance of the
previous letter, it looks awkward in its character literal form (#\name)
since it modified the backslash.  This instead prints the combining
character on a small circle.

* libguile/chars.h (SCM_CODEPOINT_DOTTED_CIRCLE): new #define

* libguile/print.c (iprint1): print combining characters on dotted circles

* libguile/read.c (scm_read_character): parse the combination of combining
  characters and dotted circles