fix talib bug on bollinger bands and other indicators when working on small assets, rise talib prescision and add test associated

freqtrade/tests/test_talib.py

@@ -0,0 +1,15 @@
+
+
+import talib.abstract as ta
+import pandas as pd
+
+def test_talib_bollingerbands_near_zero_values():
+    inputs = pd.DataFrame([
+        {'close': 0.00000010},
+        {'close': 0.00000011},
+        {'close': 0.00000012},
+        {'close': 0.00000013},
+        {'close': 0.00000014}
+    ])
+    bollinger = ta.BBANDS(inputs, matype=0, timeperiod=2)
+    assert (bollinger['upperband'][3] != bollinger['middleband'][3])