Switch from npm to yarn

Using lerna with npm breaks various npm commands such as "outodated"
etc.

Switch yarn with namespaces. lerna is only used to run commands on all
packages and maybe publish them etc. yarn 2.x has extra workspace features
like running commands for all packages, so with 2.0 we might also get
rid of lerna.

README.md

@@ -3,13 +3,12 @@
 ## Setup
 
 ```
-npm install
-npm run bootstrap
+yarn install
 ```
 
-`cd packges/some-package` and continue development with `npm run watch` etc.
+`cd packges/some-package` and continue development with `yarn run watch` etc.
 
 ## Other commands
 
-* `npm run test` -  Run test for all packages`
-* `npm run clean` - Removes all `node_modules` directories, run `bootstrap` to create them again
+* `yarn run test` -  Run test for all packages`
+* `yarn run clean` - Removes all `node_modules` directories.

lerna.json

@@ -2,5 +2,7 @@
   "packages": [
     "packages/*"
   ],
-  "version": "0.0.0"
+  "npmClient": "yarn",
+  "version": "independent",
+  "useWorkspaces": true
 }

package.json

@@ -4,9 +4,10 @@
   "description": "",
   "main": "index.js",
   "private": true,
+  "workspaces": [
+    "packages/*"
+  ],
   "scripts": {
-    "bootstrap": "lerna bootstrap --hoist --force-local --strict",
-    "clean": "lerna clean -y",
     "test": "lerna run test"
   },
   "author": "",