Fix UnmarshalFeature

- GeometryCollection cannot unmarshal

wkb scanner: support hex encoded data from go-pg

add go.mod

encoding/wkb: only limit multi allocations not read length

encoding/wkb.Value: nil geom should return nil driver.Value

add some more planar area tests and comments

fix travis, 1.10 yaml....

fix travis, 1.10 yaml....