petascope should use encode() function

[Peter Baumann]

The rasql encode() function provides comprehensive format support. Petascope currently uses the old, deprecated rasql functions png(), jpeg(), etc. This limits petascope and introduces incoherent handling of formatting parameters, due to the different handling in the latter functions vs encode().

[Dimitar Misev]

Petascope uses encode(), it only uses csv() directly from the old rasql functions. Looks like an invalid ticket to me.