Fix code coverage so it maps to TS sources (#1043)

* Fix coverage so it maps to .ts

upgrade from istanbul to nyc

use a remapper script to remap from ./node_modules/ts-node to our source tree,
since all coverage is captured from an `npm install`ed instance of ts-node

* remove commented-out code

Author: cspotcode

.gitignore

@@ -1,4 +1,5 @@
 node_modules/
+.nyc_output/
 coverage/
 .DS_Store
 npm-debug.log

nyc.config.js

@@ -0,0 +1,12 @@
+module.exports = {
+  all: true,
+  include: [
+    'tests/node_modules/ts-node/**',
+  ],
+  exclude: [
+    '**/*.d.ts',
+    'tests/node_modules/ts-node/node_modules/**',
+  ],
+  excludeNodeModules: false,
+  excludeAfterRemap: false
+};