Add tests for importers (#56)

This also fixes deep copy import for Instruments when copying from Instruments 7

Related to #14

sample/programs/ruby/simple.rb

@@ -0,0 +1,35 @@
+require 'json'
+require 'stackprof'
+
+def a
+  for i in 0..100 do
+    b
+    c
+  end
+end
+
+def b
+  for i in 0..10
+    d
+  end
+end
+
+def c
+  for i in 0..10
+    d
+  end
+end
+
+def d
+  prod = 1
+  for i in 1..1000
+    prod *= i
+  end
+  prod
+end
+
+profile = StackProf.run(mode: :wall, raw: true) do
+  a
+end
+
+puts JSON.generate(profile)