Add absolutely minimal implementation of chunking

dagger/chunking.nim

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+import ./merkledag
+
+export merkledag
+
+proc createChunks*(file: File): MerkleDag =
+  let contents = file.readAll()
+  MerkleDag(data: cast[seq[byte]](contents))
+
+proc assembleChunks*(dag: MerkleDag, output: File) =
+  output.write(cast[string](dag.data))

dagger/merkledag.nim

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+type
+  MerkleDag* = object
+    data*: seq[byte]

tests/testChunking.nim

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+import std/unittest
+import std/os
+import pkg/dagger/chunking
+
+suite "chunking":
+
+  var input, output: File
+
+  setup:
+    input = open("tests/input.txt", fmReadWrite)
+    output = open("tests/output.txt", fmReadWrite)
+    input.write("foo")
+    input.setFilePos(0)
+
+  teardown:
+    input.close()
+    output.close()
+    removeFile("tests/input.txt")
+    removeFile("tests/output.txt")
+
+  test "creates a Merkle DAG from a file":
+    check createChunks(input) != MerkleDag.default
+
+  test "creates a file from a Merkle DAG":
+    let dag = createChunks(input)
+    assembleChunks(dag, output)
+
+    input.setFilePos(0)
+    output.setFilePos(0)
+    check output.readAll() == input.readAll()
+