Moved Python to sub-directories

diff --git a/testing/dna.py b/testing/dna/dna.py
similarity index 100%
rename from testing/dna.py
rename to testing/dna/dna.py

diff --git a/testing/cdna.py b/testing/exercise/cdna.py
similarity index 100%
rename from testing/cdna.py
rename to testing/exercise/cdna.py

diff --git a/testing/test_cdna.py b/testing/exercise/test_cdna.py
similarity index 100%
rename from testing/test_cdna.py
rename to testing/exercise/test_cdna.py