Fix variable names with digits, ERL, update docs

- Tokenizer now copies entire identifier (letters+digits) when no
  keyword matches, fixing variables like K2, V1, AB3%
- ERL returns actual error line number instead of 0
- Update README and Sphinx docs for v0.5.0

src/eval.c

@@ -833,7 +833,7 @@ static gw_value_t eval_atom(void)
         gw_chrget();
         gw_value_t v;
         v.type = VT_INT;
-        v.ival = 0;
+        v.ival = gw.err_line_num;
         return v;
     }
     if (tok == TOK_ERR) {

src/tokenizer.c

@@ -137,6 +137,17 @@ int gw_crunch(const char *text, uint8_t *out, int outsize)
                     in_data = 1;
                 continue;
             }
+
+            /* Not a keyword: copy entire variable name (letters + digits) */
+            while (isalnum((unsigned char)text[ip]) || text[ip] == '.') {
+                out[op++] = text[ip++];
+                if (op >= outsize - 2) break;
+            }
+            /* Copy type suffix if present */
+            if (text[ip] == '%' || text[ip] == '!' ||
+                text[ip] == '#' || text[ip] == '$')
+                out[op++] = text[ip++];
+            continue;
         }
 
         /* &H hex, &O octal, & octal */