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.

include/engrave.h

@@ -6,11 +6,14 @@
 #ifndef ENGRAVE_H
 #define ENGRAVE_H
 
+enum engraving_texts { actual_text, remembered_text, pristine_text, text_states };
+
 struct engr {
     struct engr *nxt_engr;
-    char *engr_txt;
+    char *engr_txt[text_states];
     coordxy engr_x, engr_y;
-    unsigned engr_lth; /* for save & restore; not length of text */
+    unsigned engr_szeach;  /* length of text including trailing NUL */
+    unsigned engr_alloc; /* for save & restore; not length of text */
     long engr_time;    /* moment engraving was (will be) finished */
     xint8 engr_type;
 #define DUST 1
@@ -25,11 +28,15 @@ struct engr {
                                 * even when hero isn't (so behaves similarly
                                 * to how Elbereth did in 3.4.3) */
     Bitfield(nowipeout, 1);    /* this engraving will not degrade */
-    /* 6 free bits */
+    Bitfield(eread, 1);        /* the engraving text has been read or felt */
+    /* 5 free bits */
 };
 
 #define newengr(lth) \
     (struct engr *) alloc((unsigned) (lth) + (unsigned) sizeof (struct engr))
 #define dealloc_engr(engr) free((genericptr_t) (engr))
 
+#define engraving_to_defsym(ep) \
+    (levl[(ep)->engr_x][(ep)->engr_y].typ == CORR ? S_engrcorr : S_engroom)
+
 #endif /* ENGRAVE_H */