Mplchart

- Added `DONCHIAN` Indicator (Donchian Channel)

- Refactored `wrappers.py` into `plotters.py`
- Single line indicators now accept a `line_style` attribute

- Added `CCI` Indicator (Commodity Channel Index)
- Added `BOP` Indicator (Balance of Power)
- Added `CMF` Indicator (Chaikin Money Flow)
- Added `MFI` Indicator (Money Flow Index)

- Replacing chart `reindex` method with `slice`. The `reindex` method will be repurposed, do not use.

- Added `ZigZag` Primitive (Experimental)
- `Price` primitive now accepts calculation items like 'hlc', 'hlcc', ...
- `Price` can now be used and composed as an indicator like in `EMA(20) Price('hlcc')`

- Added `ALMA` Indicator (Arnaud Legoux Moving Average)
- Added `KELTNER` indicator (Keltner Channel)
- Added `get_series` method to `Indicator` as a wrapper to `utils.get_series`