[Geany] comments in filetypes.common

[John Gabriele]

In filetypes.common, regarding the comments for the white_space
setting, for clarity, you might change them from:

# the third argument defines whether to use the foreground colour or
use the default value defined by the filetypes
# the fourth argument defines whether to use the background colour or
use the default value defined by the filetypes

to:

# Third argument: if true, use this foreground color. If false, use
the default value defined by the filetypes.
# Fourth argument: if true, use this background color. If false, use
the default value defined by the filetypes.

---John