Refactor source layout

Introduce compat source sets and move all kotlin sources to the main directory

[no changelog]

src/main/kotlin/util/SequenceUtil.kt

@@ -0,0 +1,11 @@
+
+
+package moe.nea.firmament.util
+
+fun <T : Any> T.iterate(iterator: (T) -> T?): Sequence<T> = sequence {
+    var x: T? = this@iterate
+    while (x != null) {
+        yield(x)
+        x = iterator(x)
+    }
+}