Add colored branch stairs

Different color for stairs that go to another dungeon branch.

Adds four new glyphs, S_br{up,dn}{stair,ladder}, which use the
same character as normal stairs/ladders, but yellow color.
In tiles, the up/down arrow is yellow-green instead of while-blue.

This feature has been around a lot and is in several different
variants, but this is implemented from scratch so tiles work too.

doc/Guidebook.mn

@@ -5274,6 +5274,10 @@ b	S_blob	(blob)
 (	S_boomright	(boomerang open right)
 \`	S_boulder	(boulder)
 \-	S_brcorn	(bottom right corner)
+>	S_brdnladder	(branch ladder down)
+>	S_brdnstair	(branch staircase down)
+<	S_brupladder	(branch ladder up)
+<	S_brupstair	(branch staircase up)
 C	S_centaur	(centaur)
 \&_	S_chain	(iron chain)
 #	S_cloud	(cloud)

doc/Guidebook.tex

@@ -5775,6 +5775,10 @@ Default                      & Symbol Name                & Description\\
 \verb@(@ & S\verb+_+boomright               &	(boomerang open right)\\
 \verb@`@ & S\verb+_+boulder                 &	(boulder)\\
 \verb@-@ & S\verb+_+brcorn                  &	(bottom right corner)\\
+\verb@>@ & S\verb+_+brdnladder              &	(branch ladder down)\\
+\verb@>@ & S\verb+_+brdnstair               &	(branch staircase down)\\
+\verb@<@ & S\verb+_+brupladder              &	(branch ladder up)\\
+\verb@<@ & S\verb+_+brupstair               &	(branch staircase up)\\
 \verb@C@ & S\verb+_+centaur                 &	(centaur)\\
 \verb@_@ & S\verb+_+chain                   &	(iron chain)\\
 \# & S\verb+_+cloud                   &	(cloud)\\

doc/fixes37.0

@@ -1092,6 +1092,7 @@ spiders will occasionally spin webs when moving around
 drinking a burning potion of oil will cure being turned into slime
 new bigroom variant, a boulder maze
 vomiting on an altar provokes the deities wrath
+branch stairs have a different glyph, show up in yellow color in tty
 
 
 Platform- and/or Interface-Specific New Features