Add icons to waypoints

[opoto]

Jeff Brower suggested:

Can you add support for <sym> tags within waypoint tags ? For example:

<wpt lat="37.391093" lon="-121.884899"><name>Costco</name><sym><costco_icon.png></sym></wpt>

In this way a symbol can be displayed (i) in addition to the waypoint name, or (ii) in place of the name, with the name appearing when the cursor hovers.

Typically symbols are small, 128x128 pixels or less. This page has an example of many commonly used icons: https://crittermap.zendesk.com/hc/en-us/articles/215563623-Icons-for-Waypoints