Parses a string containing debugging options into a guint containing bit flags.
This is used within GDK and GTK+ to parse the debug options passed on the command line or through environment variables.
string is equal to "all", all flags are set. Any flags specified along with "all" in
string are inverted; thus,
"all,foo,bar" or "foo,bar,all" sets all flags except those corresponding to "foo" and "bar".
string is equal to "help", all the available keys in
keys are printed out to standard error.
pointer to an array of DebugKey which associate strings with bit flags.
the number of DebugKeys in the array.
a list of debug options separated by colons, spaces, or commas, or null.
the combined set of bit flags.