Support pixel orientated output at different resolutions

[chris-little]

@tomkralidis This was part of Issue #25, whihc I have closed, replaced by three separate issues.

I am not sure that this is easy to do at lower resolutions, unless for a very simplified symbol set. I chose the orginal 55 x 55 coordinate system as the smallest that would give reasonable reproduction of all the symbols. The most complicated symbol is probably Present Weather, ww = 94, Present weather reported from a manned weather station: Moderate or heavy snow, or rain and snow mixed or hail***, at time of observation, thunderstorm during the preceding hour but not at time of observation.

I doubt if this could meaningfully be presented at less than 21 x 21 pixels. An odd number of pixels are needed in both x and y directions as many symbols are symmetric in those dimensions or have an obvious centre point. Simpler symbols, such as Past Weather, could be done on a smaller pixel array.

Modern screens, such as on a phone typically have >400dpi, and greater than 2000 x 1000 pixels, so could theoretically display ~3000 such symbols, so it is not clear whether lower resolution pixel orientated symbols are of benefit.

So what is the use case?