Fix adding some minimal intelligence to conditional parser. See roff.7

for what's supported.  This simplified the roff_cond() function quite
nicely.  From a bug report by uqs@.

Added regression test based on bug-report example by uqs@.

Also added ROFF_DEBUG to see what the hell the parser is actually doing.
Obviously turned off by default.

1 files changed, 13 insertions, 2 deletions

diff --git a/roff.7 b/roff.7
index 469b5765..58fb4d19 100644
--- a/roff.7
+++ b/roff.7
@@ -173,8 +173,19 @@ BODY...
 BODY
 .Ed
 .Pp
-COND is a conditional (for the time being, this always evaluates to
-false).
+COND is a conditional statement.
+roff allows for complicated conditionals; mandoc is much simpler.
+At this time, mandoc supports only
+.Sq n ,
+evaluating to true;
+and
+.Sq t ,
+.Sq e ,
+and
+.Sq o ,
+evaluating to false.
+All other invocations are read up to the next end of line or space and
+evaluate as false.
 .Pp
 If the BODY section is begun by an escaped brace
 .Sq \e{ ,