(test): add nyc test coverage reporting NOT WORKING see #6

- also output source map files for nyc to use
  - (deps): add exorcist to browserify for this

- FIXME: currently bugging out:
  - browserify is not reading source maps or build folder at all?
  - webpack is reading source maps, but isn't excluding physi.js files

.gitignore

@@ -1,4 +1,5 @@
 build/
+.nyc_output/
 
 ### Node ###
 

nyc.config.js

@@ -0,0 +1,10 @@
+module.exports = {
+  exclude: [
+    // no physijs code
+    './physi.js',
+    './physijs_worker.js',
+    // no tests or test helpers
+    '*.spec.js',
+    'test-utils/**'
+  ]
+}