pass sample maps directly

[felixroos]

hey!

as already said in the discord: it would be nice if sample maps could be passed directly to WebDirt constructor, instead of an url. This would allow skipping a request if the sample map is known + enables the use case of specifying sample lists that are not available as a file on some server.

example:

new WebDirt.WebDirt({
 sampleMap: {
  bd: ['808bd/BD0000.WAV'],
  sd: ['808sd/SD0010.WAV','808sd/SD0050.WAV'],
  hh: ['hh/000_hh3closedhh.wav']
 },
 sampleMapBaseUrl:'https://raw.githubusercontent.com/tidalcycles/Dirt-Samples/master/'
});

sampleMapBaseUrl would be a nice to have.