add ode solver, tests and update docs

tests/test_fit.py

@@ -0,0 +1,16 @@
+import unittest
+
+import os
+import sys
+sys.path.insert(0, os.path.abspath('../src'))
+import fit
+
+
+class TestFit(unittest.TestCase):
+
+  def test_property(self):
+    self.assertEqual()
+
+
+if __name__ == '__main__':
+  unittest.main()