⚡ several updates.

1. merge `--chkpath` `-cp` with `-d`

2. complete test/ppmgen.nas

3. update comments about why we don't use `atof` to convert string to
number

4. update .gitignore

test/ppmgen.nas

@@ -1,20 +1,24 @@
 var RD=func(i,j){
-    return chr(bits.u32_and(255,j*0.25+i*0.001));
+    return bits.u32_and(255,j/255*255.999);
 }
 var GR=func(i,j){
-    return chr(bits.u32_and(255,j*0.15));
+    return bits.u32_and(255,i/255*255.999);
 }
 var BL=func(i,j){
-    return chr(bits.u32_and(255,j*0.05));
+    return bits.u32_and(255,0.25*255.999);
 }
 var pixel_write=func(fd,i,j){
-    var color=RD(i,j)~GR(i,j)~BL(i,j);
+    var color=RD(i,j)~" "~GR(i,j)~" "~BL(i,j)~" ";
     io.write(fd,color);
 }
 
 var fd=io.open("a.ppm","wb");
-io.write(fd,"P6\n512 512\n255\n");
-for(var i=0;i<512;i+=1)
-    for(var j=0;j<512;j+=1)
+# P3 use ASCII number
+# P6 use binary character
+io.write(fd,"P3\n256 256\n255\n");
+for(var i=255;i>=0;i-=1){
+    for(var j=0;j<256;j+=1)
         pixel_write(fd,i,j);
+    io.write(fd,"\n");
+}
 io.close(fd);