Fix dashes in preamable

Fixes https://todo.sr.ht/~sircmpwn/scdoc/9

src/main.c

@@ -47,7 +47,7 @@ static void parse_preamble(struct parser *p) {
 	struct tm *now_tm = localtime(&now);
 	strftime(date, sizeof(date), "%F", now_tm);
 	while ((ch = parser_getch(p)) != UTF8_INVALID) {
-		if (ch < 0x80 && isalnum(ch)) {
+		if ((ch < 0x80 && isalnum(ch)) || ch == '_' || ch == '-') {
 			assert(str_append_ch(name, ch) != -1);
 		} else if (ch == '(') {
 			section = parse_section(p);

test/preamble

@@ -15,7 +15,7 @@ end 1
 
 begin "Expects name to alphanumeric"
 scdoc <<EOF >/dev/null
-____(8)
+!!!!(8)
 EOF
 end 1
 
@@ -42,3 +42,9 @@ scdoc <<EOF | grep '^\.TH "test" "8" "'"$(date +'%F')"'"' >/dev/null
 test(8)
 EOF
 end 0
+
+begin "Preserves dashes"
+scdoc <<EOF | grep '^\.TH "test-manual" "8" "'"$(date +'%F')"'"' >/dev/null
+test-manual(8)
+EOF
+end 0