New Flash API, and nice surprise for Pico owners!

Hi Gordon,

Running this code:

// Flashtest

function gen_256() {
    var i;
    var str='';
    for(i=0;i<256;i++) {
        str+='X';
    }
    return(str);
}

var bytes256=gen_256();
var f = require("Flash");
var freeFlash = process.memory().flash_start + 511*1024;
console.log(f.getPage(freeFlash));
console.log('LEN:'+bytes256.length);
f.erasePage(freeFlash);
console.log('Nr.1, at '+freeFlash);
f.write(bytes256, freeFlash);
freeFlash+=256;
console.log('Nr.2, at '+freeFlash);
f.write(bytes256, freeFlash);
freeFlash+=256;
console.log('Nr.3, at '+freeFlash);
f.write(bytes256, freeFlash);
freeFlash+=256;
console.log('Nr.4, at '+freeFlash);
f.write(bytes256, freeFlash);
freeFlash+=256;
console.log('Nr.5, at '+freeFlash);
f.write(bytes256, freeFlash);
freeFlash+=256;
console.log('Nr.6, at '+freeFlash);
f.write(bytes256, freeFlash);
freeFlash+=256;
console.log('Nr.7, at '+freeFlash);
f.write(bytes256, freeFlash);