Nyall Dawson ac0326a351 [API] Add useful PyQGIS additions to QgsSymbol
Adds:
- __len__ : returns number of symbol layers in symbol
- [ ] getter: returns a specific symbol layer, also allows negative indices to retrieve from end of symbol
- del [ ]: removes a specific symbol layer, also allows negative indices
- raise IndexError when an invalid symbol layer is requested
- allow iteration over symbol layers using
  for layer in symbol:
     print(layer.color())
2019-07-08 08:41:59 +10:00
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