added function that procedurally generates heightfield

[demo] / external / libimago

diff --git a/external/libimago b/external/libimago
index d7e3914..843ac48 160000 (submodule)
--- a/external/libimago
+++ b/external/libimago
@@ -1 +1 @@
-Subproject commit d7e3914d568a9e397b1bcd11b3722a84e7f4334e
+Subproject commit 843ac48c7cd58166bb9dc0d49097c1b0ae7e2029