Remove redundant loss.replace, add constants for magic numbers, document threading safety

alpaca_trader/indicators.py

@@ -10,7 +10,6 @@ def rsi(data, window=14):
     delta = data.diff()
     gain = (delta.where(delta > 0, 0)).rolling(window=window).mean()
     loss = (-delta.where(delta < 0, 0)).rolling(window=window).mean()
-    loss = loss.replace(0, 1e-10)
     loss = loss.clip(lower=1e-10)
     rs = gain / loss
     rsi_val = 100 - (100 / (1 + rs))