remove support for TOML and JSON

ref #34

example/Taskfile.json

@@ -1,11 +0,0 @@
-{
-  "hello": {
-    "cmds": [
-      "echo \"I am going to write a file named 'output.txt' now.\"",
-      "echo \"hello\" > output.txt"
-    ],
-    "generates": [
-      "output.txt"
-    ]
-  }
-}

example/Taskfile.toml

@@ -1,6 +0,0 @@
-[hello]
-cmds = [
-  "echo \"I am going to write a file named 'output.txt' now.\"",
-  "echo \"hello\" > output.txt"
-]
-generates = ["output.txt"]