1.19.0

Modified indicators:

• add Beta+/Beta- to Beta - #597
• add slow and fast EMA to MACD results - #595

Modify supported frameworks:

• add .NET 6.0
• remove .NET Framework 4.6.1

Chores:

• add simple backtest example code

Special thanks to:

• @GordonEldest for recommending Beta+/-
• @sophisma for recommending EMA additions to MACD