unit test for #100

unittest: the check macro will print only the non-literal part of the checked expression
tests/run: added tunittests.nim as a single central executable where unittests could be added for quicker compilation/execution of the test suite

tests/run/tunittests.nim

@@ -0,0 +1,2 @@
+import uclosures
+

tests/run/uclosures.nim

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+import unittest
+
+test "loop variables are captured by copy":
+  var funcs: seq[proc (): int {.closure.}] = @[]
+  
+  for i in 0..10:
+    funcs.add do -> int: return i * i
+
+  check funcs[0]() == 0
+  check funcs[3]() == 9
+