Printed output is stripped of spaces

[balaziks]

?-write(' '), write('test'), write(' '). prints only test to the output window.

This (together with #119) makes for example pretty-printing trees like this

    g
  c
    f
a
    e
  b
    d

rather inconvenient.

[JeanChristopheRohner]

An option is to use html/1 to print some white characters, like this:
html(span(style('color:rgb(255, 255, 255)'), 'xxxx')
Hope that helps!