a few possible additions

a few possible additions for fontello/svg-font-dump:

added DumpSVG() to make it work as a module
added -x option to save with just numeric filenames
added MakeDirectory(fp) to make the args.glyphs_dir directory tree if it isn't present
added usage examples for use as a module in node code, and from the CLI

see mainly
if(require.main!=module){/*Use as a module*/module.exports={DumpSVG:DumpSVG}
}else{/*Use from the command line*/ 
}
went through git hell to make this PR (as is my 1st attempt at such, hope it worked)

good work!! thanks for the svg font tools