Enable generating specific themed rooms for debugging

A common pain point I encounter when working on themed rooms is making
specific rooms generate. The only ways to do this were mass commenting
out the rooms not being tested, or hacking in different room frequency
values (even more annoying when testing a fill, not a room, or testing
pure-function rooms/fills that have no frequency).

This change solves that problem by allowing a wizard-mode user to define
THEMERM or THEMERMFILL environment variables to make specific rooms or
fills generate.

The first part of this change is converting all themed rooms and fills
that were plain functions into tables, and converting their comment
names into actual names in those tables. The names are not intended to
be shown during gameplay, but instead serve as values that THEMERM or
THEMERMFILL can be matched to to generate those rooms. It's no longer
possible to have a function themeroom; this will raise an impossible.
As far as I'm concerned, this is a good change because it allows some
code simplification of themerooms_generate and makes it easier to add
difficulty or eligibility parameters to rooms.

The second part of this change is adding a new nh.debug_themerm function
to make the environment variable values accessible to themerms.lua. I
looked for an existing way to do this but didn't see one (nh.variable
is the closest but appears to be for variables that get saved).

The final part is inserting behavior into the actual themeroom
generation code that changes how they generate when either a room or a
fill is set. I don't think it's safe to generate every single room with
the requested type or fill - that might lead to cases where the stairs
or a magic portal cannot generate. So it creates ordinary rooms half of
the time, which still results in plenty of themed rooms on levels.

Another thing to note is that any themed room using filler_region will
still only pick a fill 30% of the time. If one specifies both a fill and
a room that uses filler_region, many of those rooms will appear without
a themed fill.

src/nhlua.c

@@ -65,6 +65,7 @@ staticfn int nhl_rn2(lua_State *);
 staticfn int nhl_random(lua_State *);
 staticfn int nhl_level_difficulty(lua_State *);
 staticfn int nhl_is_genocided(lua_State *);
+staticfn int nhl_get_debug_themerm_name(lua_State *);
 staticfn void init_nhc_data(lua_State *);
 staticfn int nhl_push_anything(lua_State *, int, void *);
 staticfn int nhl_meta_u_index(lua_State *);
@@ -975,6 +976,30 @@ nhl_is_genocided(lua_State *L)
     return 1;
 }
 
+/* local debug_themerm = nh.debug_themerm(isfill)
+ * if isfill is false, returns value of env variable THEMERM
+ * if isfill is true,  returns value of env variable THEMERMFILL
+ * return nil if not in wizard mode or the variable isn't set */
+staticfn int
+nhl_get_debug_themerm_name(lua_State *L)
+{
+    int argc = lua_gettop(L);
+    if (argc == 1) {
+        char *dbg_themerm = (char *) 0;
+        boolean is_fill = lua_toboolean(L, 1);
+        lua_pop(L, 1);
+        if (wizard)
+            dbg_themerm = getenv(is_fill ? "THEMERMFILL" : "THEMERM");
+        if (!dbg_themerm || strlen(dbg_themerm) == 0) {
+            lua_pushnil(L);
+        } else {
+            lua_pushstring(L, dbg_themerm);
+        }
+    } else {
+        nhl_error(L, "debug_themerm should have 1 boolean arg");
+    }
+    return 1;
+}
 
 RESTORE_WARNING_UNREACHABLE_CODE
 
@@ -1754,6 +1779,7 @@ static const struct luaL_Reg nhl_functions[] = {
     { "random", nhl_random },
     { "level_difficulty", nhl_level_difficulty },
     { "is_genocided", nhl_is_genocided },
+    { "debug_themerm", nhl_get_debug_themerm_name },
     { "parse_config", nhl_parse_config },
     { "get_config", nhl_get_config },
     { "get_config_errors", l_get_config_errors },