Datalog (#233)

* support for custom csv separator

* simple datalog frameowrk

* api strings

* hide setfile

* storage fixes

* log seconds, not milliseconds

libs/datalog/pxt.json

@@ -0,0 +1,16 @@
+{
+    "name": "datalog",
+    "description": "Tiny data logging framework",
+    "files": [
+        "README.md",
+        "datalog.ts"
+    ],
+    "testFiles": [
+        "test.ts"
+    ],
+    "public": true,
+    "dependencies": {
+            "core": "file:../core",
+            "storage": "file:../storage"
+    }
+}