build(aio): truncate API overview parameters at one line

aio/tools/transforms/angular-base-package/rendering/truncateFirstLine.js

@@ -0,0 +1,13 @@
+module.exports = function() {
+  return {
+    name: 'truncateFirstLine',
+    process: function(str) {
+      const parts = str && str.split && str.split(/\r?\n/);
+      if (parts && parts.length > 1) {
+        return parts[0] + '...';
+      } else {
+        return str;
+      }
+    }
+  };
+};

aio/tools/transforms/angular-base-package/rendering/truncateFirstLine.spec.js

@@ -0,0 +1,19 @@
+var factory = require('./truncateFirstLine');
+
+describe('truncateFirstLine filter', function() {
+  var filter;
+
+  beforeEach(function() { filter = factory(); });
+
+  it('should be called "truncateFirstLine"',
+     function() { expect(filter.name).toEqual('truncateFirstLine'); });
+
+  it('should return the whole string if only one line', function() {
+    expect(filter.process('this is a pretty long string that only exists on one line'))
+      .toEqual('this is a pretty long string that only exists on one line');
+  });
+
+  it('should return the first line and an ellipsis if there is more than one line', function() {
+    expect(filter.process('some text\n  \nmore text\n  \n')).toEqual('some text...');
+  });
+});