add donut fun test

test/donut.c

@@ -0,0 +1,20 @@
+             i,j,k,x,y,o,N;
+         main(){float z[1760],a
+      #define R(t,x,y) f=x;x-=t*y\
+   ;y+=t*f;f=(3-x*x-y*y)/2;x*=f;y*=f;
+   =0,e=1,c=1,d=0,f,g,h,G,H,A,t,D;char
+ b[1760];for(;;){memset(b,32,1760);g=0,
+h=1;memset(z,0,7040);for(j=0;j<90;j++){
+G=0,H=1;for(i=0;i<314;i++){A=h+2,D=1/(G*
+A*a+g*e+5);t=G*A        *e-g*a;x=40+30*D
+*(H*A*d-t*c);y=          12+15*D*(H*A*c+
+t*d);o=x+80*y;N          =8*((g*a-G*h*e)
+*d-G*h*a-g*e-H*h        *c);if(22>y&&y>
+ 0&&x>0&&80>x&&D>z[o]){z[o]=D;b[o]=(N>0
+  ?N:0)[".,-~:;=!*#$@"];}R(.02,H,G);}R(
+  .07,h,g);}for(k=0;1761>k;k++)putchar
+   (k%80?b[k]:10);R(.04,e,a);R(.02,d,
+     c);usleep(15000);printf('\n'+(
+        " donut.c! \x1b[23A"));}}
+          /*no math lib needed
+             .@a1k0n 2021.*/