Update README
Add Achavi link
fix #8 - support WKT polygons in RSS feed

This allows to specify non-rectangular bboxes.

Rectangular example (lat/lon have to be multiplied with factor 100):
rss.php?wkt=POLYGON((4600 1200, 4700 1200, 4700 1300, 4600 1300, 4600 1200))
Merge remote-tracking branch 'simon04/develop'