v0.4.0 beta - Memory usage and texures improvements.

A fiew tweaks to improve memory usage:

use parameter --threads 1 --maxqueue 1 to limit memory usage.

This version also includes two pull requests:

Significantly improve memory usage when rendering zoom levels
#21 by barrett777 was merged 5 days ago
Fixed bunch of annoyances, e.g.:
#19 by jflin404 was merged 5 days ago

Thx for the help!
Thx to Mecu for updating the docs!