Useful Path operations for filesytem. (#153)

Summary:
Includes the previously accepted changes to Path for "Relative path functions and equality for Path.t"
Combining with this diff to minimize Shipit thrash (had problems with other diff)

Includes many test cases but not enough.
Pull Request resolved: #153

Reviewed By: kyldvs

Differential Revision: D15011790

Pulled By: jordwalke

fbshipit-source-id: 7538fcbc6fd2a6fd7e1ce696928c300a6657c66e

ORIGINS.md

@@ -0,0 +1,9 @@
+
+
+Thanks to the following libraries for being useful as references/guides for how
+to handle various system/terminal integration.
+
+- [bos](https://github.com/dbuenzli/bos) For demonstrating how to correctly and
+  robustly handle `Unix` exceptions. It is a great reference for which `Unix`
+  exceptions are raised for which operations, and demonstrates the robust
+  pattern of reattempts on interupt exceptions.

esy.json

@@ -8,6 +8,8 @@
     "install": [
       "esy-installer pastel.install",
       "esy-installer rely.install",
+      "esy-installer path.install",
+      "esy-installer fs.install",
       "esy-installer console.install",
       "esy-installer pastel-console.install",
       "esy-installer file-context-printer.install",

fs.json

@@ -0,0 +1,37 @@
+{
+  "name": "@reason-native/fs",
+  "version": "0.0.1",
+  "description": "Reason Native file system API",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/facebookexperimental/reason-native/tree/master/src/fs"
+  },
+  "license": "MIT",
+  "keywords": [
+    "file-system",
+    "fs",
+    "filesystem",
+    "directories",
+    "reasonml",
+    "reason",
+    "ocaml",
+    "esy"
+  ],
+  "esy": {
+    "build": "dune build -p fs"
+  },
+  "scripts": {
+    "release": "node ./scripts/esy-prepublish.js fs.json"
+  },
+  "dependencies": {
+    "@reason-native/path": ">= 0.0.0 <= 1.0.0",
+    "@opam/dune": "*",
+    "@esy-ocaml/reason": "*",
+    "ocaml": "^4.2.0"
+  },
+  "devDependencies": {
+    "@opam/merlin": "*",
+    "ocaml": "~4.6.0",
+    "@reason-native/rely": "*"
+  }
+}

src/fs/Fs.re

@@ -0,0 +1,13 @@
+/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ */;
+
+/*
+Fs: Reason native filesystem utilities.
+*/
+include Types;
+include Traverse;
+include ReadWriteContents;
+include Operations;
+include Query;
+include Perm;