Grammar: Add 'c' to compass point values

src/dot.test.js

@@ -241,6 +241,12 @@ describe('dot.DotGraph.toString()', () => {
     expect(screen.getByTestId('dot-src').textContent).toBe(dotSrc);
   });
 
+  it('accepts "c" as a compass point on nodes', () => {
+    let dotSrc = 'digraph {a:p1:c}';
+    render(<WrapDot dotSrc={dotSrc} />);
+    expect(screen.getByTestId('dot-src').textContent).toBe(dotSrc);
+  });
+
   it('renders nodes with names equal to properties of the Javascript Object', () => {
     const nodeNames = getAllPropertyNames({});
     const dotSrc = `digraph {${nodeNames.join(' ')}}`;
@@ -286,6 +292,12 @@ describe('dot.DotGraph.toString()', () => {
     expect(screen.getByTestId('dot-src').textContent).toBe(dotSrc);
   });
 
+  it('renders an edge directed at the center point of two nodes', () => {
+    let dotSrc = 'digraph {a:p1:c -> b:p2:c}';
+    render(<WrapDot dotSrc={dotSrc} />);
+    expect(screen.getByTestId('dot-src').textContent).toBe(dotSrc);
+  });
+
   // nodes and edges
 
   it('renders multiple nodes and edges', () => {

src/dotGrammar.pegjs

@@ -151,7 +151,7 @@ subgraph
       }
 
 compass_pt
-  = 'n'/'ne'/'e'/'se'/'s'/'sw'/'w'/'nw'
+  = 'n'/'ne'/'e'/'se'/'s'/'sw'/'w'/'nw'/'c'
 
 ID
   = STRING