New player commands: decrease/increase tempo factor.

It would be nice to have player commands to increase/decrease the relative tempo factor. This requires updating to libxmp 4.7.0, so no milestone currently assigned. Proof-of-concept patch via https://github.com/libxmp/libxmp/pull/966:

diff --git a/src/commands.c b/src/commands.c
index 9b4a8239..6266a402 100644
--- a/src/commands.c
+++ b/src/commands.c
@@ -145,6 +145,7 @@ static void change_sequence(xmp_context handle, const struct xmp_module_info *mi
  */
 void read_command(xmp_context handle, const struct xmp_module_info *mi, struct control *ctl)
 {
+	double factor;
 	int cmd;
 
 	cmd = read_key();
@@ -276,5 +277,23 @@ void read_command(xmp_context handle, const struct xmp_module_info *mi, struct c
 	case '<':
 		change_sequence(handle, mi, ctl, -1);
 		break;
+	case '[':
+		factor = xmp_get_tempo_factor_relative(handle);
+		if (factor >= 0.2) {
+			factor -= 0.1;
+			if (xmp_set_tempo_factor_relative(handle, factor) == 0) {
+				info_message("Time factor %.02f", factor);
+			}
+		}
+		break;
+	case ']':
+		factor = xmp_get_tempo_factor_relative(handle);
+		if (factor > 0.0) {
+			factor += 0.1;
+			if (xmp_set_tempo_factor_relative(handle, factor) == 0) {
+				info_message("Time factor %.02f", factor);
+			}
+		}
+		break;
 	}
 }

Start in src/commands.c and review the libxmp 4.7.0 update requirement, using the referenced libxmp pull request as context. The work is done when player commands can increase and decrease the relative tempo factor and report the resulting factor.