Add tasks for all the new languages

Task/Variables/Pony/variables-1.pony

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+var counter: I32 = 10 // mutable variable 'counter' with value 10
+let temp: F64 = 36.6  // immutable variable 'temp'
+let str: String       // immutable variable 'str' with no initial value
+str = "i am a string" // variables must be initialized before use
+let another_str = "i am another string" // type of variable 'another_str' infered from assigned value
+
+let b  = true
+let b' = false // variable names can contain ' to make a distinct variable with almost the same name

Task/Variables/Pony/variables-2.pony

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+var x: I32 = 10
+var y: I32 = x = 20
+try
+  Fact(x == 20) // x gets the new value of 20
+  Fact(y == 10) // y gets the old value of x which is 10
+end