Add support for multi-level includes and cyclic include detection

testdata/includes_cycle/Taskfile.yml

@@ -0,0 +1,12 @@
+version: '3'
+
+includes:
+  'one': ./one/Taskfile.yml
+
+tasks:
+  default:
+    cmds:
+      - echo "called_dep" > called_dep.txt
+  level1:
+    cmds:
+      - echo "hello level 1"

testdata/includes_cycle/one/Taskfile.yml

@@ -0,0 +1,9 @@
+version: '3'
+
+includes:
+  'two': ./two/Taskfile.yml
+
+tasks:
+  level2:
+    cmds:
+      - echo "hello level 2"

testdata/includes_cycle/one/two/Taskfile.yml

@@ -0,0 +1,9 @@
+version: '3'
+
+includes:
+  bad: "../../Taskfile.yml"
+
+tasks:
+  level3:
+    cmds:
+      - echo "hello level 3"