add custom Cmd and Dep types

testdata/params/.gitignore

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+*.txt

testdata/params/Taskfile.yml

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+default:
+  deps:
+    - task: write-file
+      params:
+        CONTENT: Dependence1
+        FILE: dep1.txt
+    - task: write-file
+      params:
+        CONTENT: Dependence2
+        FILE: dep2.txt
+  cmds:
+    - task: write-file
+      params:
+        CONTENT: Hello
+        FILE: hello.txt
+    - task: write-file
+      params:
+        CONTENT: World
+        FILE: world.txt
+    - task: write-file
+      params:
+        CONTENT: "!"
+        FILE: exclamation.txt
+
+write-file:
+  cmds:
+    - echo {{.CONTENT}} > {{.FILE}}