colour markers by:

• year
• month
• year+month
• nothing

hide unselected markers
add marker outlines for better visibility

filter by dates (click to expand):

	01	02	03	04	05	06	07	08	09	10	11	12
2012	01	02	03	04	05	06	07	08	09	10	11	12
2013	01	02	03	04	05	06	07	08	09	10	11	12
2014	01	02	03	04	05	06	07	08	09	10	11	12

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