Support drives other than C:\ on Windows

Edited `filesystem.js` functions to support Windows drives
- `getDirectoryContents` shows a list of Windows drives when requested `/` root path
- Subsequent paths will be formatted as `/<drive letter>/<path>`. Eg. `/c/Users/neojp/Desktop/archive.bcup`
- A new function `normalizeWindowsPath` will convert server request paths into resolved Windows paths
  `/c/Users/neojp/Desktop/archive.bcup` -> `c:\\Users\\neojp\\Desktop\\archive.bcup`

Fixes buttercup#3

source/filesystem.js

@@ -9,19 +9,25 @@ const stat = pify(fs.stat);
 const writeFile = pify(fs.writeFile);
 
 const FILES_TO_HIDE = /^\./;
+const IS_WINDOWS = process.platform === 'win32';
 
 function getDirectoryContents(dir) {
-    return readDir(dir)
+    if (IS_WINDOWS && dir === '/') {
+        return handleWindowsRootPath();
+    }
+
+    let dirRealPath = normalizePath(dir);
+    return readDir(dirRealPath)
         .then(contents => Promise.all(contents.map(filename =>
-            stat(path.join(dir, filename))
+            stat(path.join(dirRealPath, filename))
                 .then(stat => ({
                     name: filename,
                     directory: dir,
                     isFile: stat.isFile(),
                     isDirectory: stat.isDirectory()
                 }))
                 .catch(err => {
-                    console.error(`Error while trying to stat file: ${path.join(dir, filename)} (${err.message})`);
+                    console.error(`Error while trying to stat file: ${path.join(dirRealPath, filename)} (${err.message})`);
                     return null;
                 })
         )))
@@ -37,11 +43,69 @@ function getDirectoryContents(dir) {
 }
 
 function getFileContents(path) {
-    return readFile(path, "utf8");
+    return readFile(normalizePath(path), "utf8");
 }
 
 function putFileContents(path, contents) {
-    return writeFile(path, contents, "utf8");
+    // windows paths must have at least 3 parts due to drive letter
+    // 2 or less parts mean script is write to a path that doesn't exist
+    if (IS_WINDOWS && path.split('/').length <= 2) {
+        return Promise.reject(new Error(`Can't write files on Windows root path`));
+    }
+    return writeFile(normalizePath(path), contents, "utf8");
+}
+
+function getWindowsDrives() {
+    return new Promise((resolve, reject) => {
+        let stdout = '';
+        let stderr;
+        const { spawn } = require('child_process'),
+            list = spawn('cmd');
+
+        list.stdout.on('data', (data) => stdout += data);
+        list.stderr.on('data', (data) => stderr += data);
+
+        list.on('exit', function (code) {
+            if (code == 0) {
+                let data = stdout.split('\r\n');
+                data = data.splice(4, data.length - 7);
+                data = data.map(drive => drive.substring(0, 1).toLowerCase());
+                resolve(data);
+            } else {
+                reject({ code, message: stderr });
+            }
+        });
+        list.stdin.write('wmic logicaldisk get caption\n');
+        list.stdin.end();
+    });
+
+}
+
+function handleWindowsRootPath(dir) {
+    return getWindowsDrives()
+        .then(drives => {
+            return drives.map(drive => {
+                return {
+                    name: drive,
+                    directory: '/',
+                    type: 'directory'
+                };
+            });
+        })
+        .catch(err => {
+            console.error(`Error while trying to get all Windows drives: (${err.message})`);
+            return null;
+        });
+}
+
+function normalizeWindowsPath(dir) {
+    const drive = dir.substring(1, 2) + ':';
+    const filePath = dir.substring(2) || '/';
+    return path.join(drive, filePath);
+}
+
+function normalizePath(dir) {
+    return (IS_WINDOWS) ? normalizeWindowsPath(dir) : dir;
 }
 
 module.exports = {