Add a second scalebar style, add cmd help for -scalebar command

src/cli/mapshaper-options.mjs

@@ -1987,13 +1987,33 @@ export function getOptionParser() {
       DEFAULT: true,
       describe: 'distance label, e.g. "35 miles"'
     })
-    .option('top', {})
-    .option('right', {})
-    .option('bottom', {})
-    .option('left', {})
-    .option('font-size', {})
-    // .option('font-family', {})
-    .option('label-position', {}); // top or bottom
+    .option('style', {
+      describe: 'two options: a or b'
+    })
+    .option('font-size', {
+      type: 'number'
+    })
+    .option('tic-length', {
+      describe: 'length of tic marks (style b)',
+      type: 'number'
+    })
+    .option('bar-width', {
+      describe: 'line width of bar',
+      type: 'number'
+    })
+    .option('label-offset', {
+      type: 'number'
+    })
+    .option('position', {
+      describe: 'e.g. bottom-right (default is top-left)'
+    })
+    .option('label-position', {
+      describe: 'top or bottom'
+    })
+    .option('margin', {
+      describe: 'offset in pixels from edge of map',
+      type: 'number'
+    });
 
   parser.command('shape')
     .describe('create a polyline or polygon from coordinates')

src/cli/mapshaper-run-command.mjs

@@ -121,6 +121,10 @@ export async function runCommand(command, job) {
     return done(null);
   }
 
+  if (name == 'comment') {
+    return done(null);
+  }
+
   if (!job) job = new Job();
   job.startCommand(command);
 

src/crs/mapshaper-projections.mjs

@@ -244,10 +244,10 @@ export function requireDatasetsHaveCompatibleCRS(arr) {
 // x, y: a point location in projected coordinates
 // Returns k, the ratio of coordinate distance to distance on the ground
 export function getScaleFactorAtXY(x, y, crs) {
-  var dist = 1;
+  var dist = 1 / crs.to_meter;
   var lp = mproj.pj_inv_deg({x: x, y: y}, crs);
   var lp2 = mproj.pj_inv_deg({x: x + dist, y: y}, crs);
-  var k = dist / geom.greatCircleDistance(lp.lam, lp.phi, lp2.lam, lp2.phi);
+  var k = 1 / geom.greatCircleDistance(lp.lam, lp.phi, lp2.lam, lp2.phi);
   return k;
 }