add screenshots and images for docs. add icon.

lib/__tests__/dimensions-test.ts

@@ -0,0 +1,14 @@
+import { diameterToLength, length_t } from '../dimensions';
+
+describe('diameterToLength', () => {
+    it('should throw an error if the units of the outer and inner diameters do not match', () => {
+        expect(() => diameterToLength({ l: 10, u: 'inch' }, { l: 8, u: 'foot' }, 2)).toThrow('diameter units must match!');
+    });
+
+    it('should return the correct length for multiple rings with different units', () => {
+        const outer : length_t = {l: 25, u: "in"};
+        const inner: length_t = {l : 1, u: "in"};
+        const l = diameterToLength(outer, inner, 12);
+        expect(l.l).toBeCloseTo(490, -1.0);
+    });
+});