sym-changes - add engravings to the map

1. Add "engraved room floor" pchar sym (S_engroom). The symbol that
displays at the engraved part of a room (not a corridor though).
The default symbol is '`' which is currently never shown if people
have defined the boulder symbol to '0' and statues are displayed as
monster symbols. It is bright blue.

Add some stylized variations of the S_engroom symset to some of
the symsets.

2. Add "engraved corridor" pchar sym (S_engrcorr). The symbol that
displays at the engraved part of a corridor. The default symbol is
'#', and it matches the symbol for corridor from for whatever the
current symset uses. It is bright blue to match the color of the
S_engroom symbol. Using the normal corridor symbol for display
preserves the lines of the corridor so is not as visually-disruptive
as a smaller symbol would be. Explicit entries that match the S_corr
symbol have been added to the symset file.

Magic mapping and clairvoyance impacts yet to be determined.

The Guidebook updates will come later.

dat/symbols

@@ -251,11 +251,13 @@ start: IBMgraphics
 	S_ndoor: \xfa			# meta-z, centered dot
 	S_vodoor: \xfe			# meta-~, small centered square
 	S_hodoor: \xfe			# meta-~, small centered square
+	S_engroom: \xee                 # epsilon
 	S_bars: \xf0			# equivalence symbol
 	S_tree: \xf1			# plus or minus symbol
 	S_room: \xfa			# meta-z, centered dot
 	S_corr: \xb0			# meta-0, light shading
 	S_litcorr: \xb1			# meta-1, medium shading
+	S_engrcorr: \xb0		# meta-0, light shading
 	S_fountain: \xf4		# meta-t, integral top half
 	S_sink: \xf4			# meta-t, integral top half
 	S_pool: \xf7			# meta-w, approx. equals
@@ -287,6 +289,7 @@ start: IBMGraphics_1
 	S_tdwall: \xc2			# meta-B, T down
 	S_tlwall: \xb4			# meta-4, T left
 	S_trwall: \xc3			# meta-C, T right
+	S_engroom: \xee                 # epsilon
 	S_vbeam: \xb3			# meta-3, vertical rule
 	S_hbeam: \xc4			# meta-D, horizontal rule
 	S_sw_ml: \xb3			# meta-3, vertical rule
@@ -311,8 +314,10 @@ start: IBMGraphics_2
 	S_trwall: \xc3			# meta-C, T right
 	S_vodoor: \xfe			# meta-~, small centered square
 	S_hodoor: \xfe			# meta-~, small centered square
+	S_engroom: \xee                 # epsilon
 	S_corr: \xb0			# meta-0, light shading
 	S_litcorr: \xb1			# meta-1, medium shading
+	S_engrcorr: \xb0		# meta-0, light shading
 	S_vbeam: \xb3			# meta-3, vertical rule
 	S_hbeam: \xc4			# meta-D, horizontal rule
 	S_sw_ml: \xb3			# meta-3, vertical rule
@@ -348,6 +353,7 @@ start: RogueIBM
 	S_room: \xfa			# centered dot
 	S_corr: \xb1
 	S_litcorr: \xb2
+	S_engrcorr: \xb1
 	S_upstair: \xf0			# Greek Xi
 	S_dnstair: \xf0
 	S_brupstair: \xf0		# Greek Xi
@@ -374,8 +380,10 @@ start: RogueEpyx
 	S_vodoor: \xce
 	S_hodoor: \xce
 	S_room: \xfa			# centered dot
+	S_engroom: \xee                 # epsilon
 	S_corr: \xb1
 	S_litcorr: \xb2
+	S_engrcorr: \xb1
 	S_upstair: \xf0			# Greek Xi
 	S_dnstair: \xf0
 	S_brupstair: \xf0		# Greek Xi
@@ -452,8 +460,10 @@ start: RogueWindows
 	S_vodoor: \xce
 	S_hodoor: \xce
 	S_room: \xfa			# centered dot
+	S_engroom: \xee                 # epsilon
 	S_corr: \xb1
 	S_litcorr: \xb2
+	S_engrcorr: \xb1
 	S_upstair: \xf0			# Greek Xi
 	S_dnstair: \xf0
 	S_brupstair: \xf0		# Greek Xi
@@ -479,8 +489,10 @@ start: curses
 	S_bars: \xfc			# meta-|, not-equals sign (was '#')
 	S_tree: \xe7			# meta-g, plus or minus sign
 	S_room: \xfe			# meta-z, centered dot
+	S_engroom: \xee                 # epsilon
 	S_corr: \xe1			# meta-a, solid block
 	S_litcorr: \xe1			# meta-a, solid block
+	S_engrcorr: \xe1			# meta-a, solid block
 	S_ice: \xfe			# meta-z, centered dot
 	S_vodbridge: \xfe		# meta-z, centered dot
 	S_hodbridge: \xfe		# meta-z, centered dot
@@ -560,6 +572,7 @@ start: MACgraphics
 	S_bars: \xf0			# equivalency symbol
 	S_tree: \xf1			# plus-or-minus
 	S_corr: \xb0
+	S_engrcorr: \xb0
 	S_grave: \xef			# same as open door
 	S_pool: \xe0
 finish
@@ -585,6 +598,7 @@ start: Enhanced1
 	S_bars: U+2261                      # IDENTICAL TO
 	S_tree: U+03a8                      # GREEK CAPITAL LETTER PSI
 	S_room: U+00b7                      # MIDDLE DOT
+	S_engroom: U+03BE                   # Greek Small Letter Xi
 	S_darkroom: U+00b7                  # MIDDLE DOT
 	S_upladder: U+2264                  # LESS-THAN OR EQUAL TO
 	S_dnladder: U+2265                  # GREATER-THAN OR EQUAL TO