Document new raster analytic and processing functions in official docs

[robe]

Document ST_Approxim* (stddev, mean, histogram etc), ST_Histogram, ST_MinMax, ST_Mean, ST_Quantile, ST_Reclass

[robe]

so far have done ST_Count, ST_Quantile, ST_Reclass, ST_Histogram, ST_SummaryStats, ST_ValueCount, ST_AsPNG, ST_AsTIFF, ST_AsGDALRaster. as of r7333. Also the helper types and I moved all the types to raster section and put in the histogram, summarystats, reclassarg (since it was too hard to have the PostgreSQL comment generator look for them in the PostGIS type section) ​http://www.postgis.org/documentation/manual-svn/RT_reference.html#Raster_Types

My main fear is with histogram that its common enough of a name that we may run into collisions later — e.g. should PostGIS geometry/geography implement such a thing or some other PostgreSQL package. Anyrate won't worry about it for now.

Still have all the ST_Approx and remaining output functions to go ST_AsJPEG etc.

I haven't really stress tested too much — the output functions I did test a bit on real world rasters but not super stress tested. I was mostly focusing on correctness. Next round after I have them documented I'll test with real world rasters. Though my general feeling with the pseudo testing I have done is that the performance is decent (well better than I would have expected for the first go round anyway).

[robe]

pretty much done with this too.