Add tasks for all the new languages

Task/File-input-output/Nim/file-input-output-1.nim

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+import os
+copyfile("input.txt", "output.txt")

Task/File-input-output/Nim/file-input-output-2.nim

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+let x = readFile("input.txt")
+writeFile("output.txt", x)

Task/File-input-output/Nim/file-input-output-3.nim

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+var
+  i = open("input.txt")
+  o = open("output.txt", fmWrite)
+
+for line in i.lines:
+  o.writeln(line)
+
+i.close()
+o.close()

Task/File-input-output/Nim/file-input-output-4.nim

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+const size = 4096
+
+var
+  i = open("input.txt")
+  o = open("output.txt", fmWrite)
+  buf: array[size, char]
+
+while i.readBuffer(buf.addr, size) > 0:
+  discard o.writeBuffer(buf.addr, size)
+
+i.close()
+o.close()

Task/File-input-output/Nim/file-input-output-5.nim

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+import memfiles
+
+var
+  i = memfiles.open("input.txt")
+  o = system.open("output.txt", fmWrite)
+
+var written = o.writeBuffer(i.mem, i.size)
+assert(written == i.size)
+
+i.close()
+o.close()