slog.c: Change level symbol to a single letter

A single symbol was added to the log depending on the level, one of ".-*#"
This had an issue: there were only 4 symbols but there are 5 levels; in
addition a `%b` was used which logged a number instead of a letter.
This commit changes the logic to add a single uppercase letter instead,
based on the level (e.g. WEBDIS_ERROR is E, _INFO is I, etc.)

src/slog.c

@@ -49,7 +49,7 @@ void
 slog(struct server *s, log_level level,
 		const char *body, size_t sz) {
 
-	const char *c = ".-*#";
+	const char *c = "EWNID";
 	time_t now;
 	struct tm now_tm, *lt_ret;
 	char time_buf[64];
@@ -77,7 +77,7 @@ slog(struct server *s, log_level level,
 
 	/* generate output line. */
 	line_sz = snprintf(line, sizeof(line),
-		"[%d] %s %d %s\n", (int)s->log.self, time_buf, c[level], msg);
+		"[%d] %s %c %s\n", (int)s->log.self, time_buf, c[level], msg);
 
 	/* write to log and flush to disk. */
 	ret = write(s->log.fd, line, line_sz);