Windows Portable App (#417)

* packager: call callbacks consistently

Before this, the callbacks would not being called, which would lead to
an incomplete build on non-OS X platforms when trying to build all for
all platforms.

* packager: Always produce OS X update file regardless of --package option

This makes it consistent with how the windows build always produces the
.nupkg autoupdate files

* packager: fix duplicate npm install

Move "npm prune && npm dedupe" into the release script. Remove an extra
"npm install"

* Make Windows portable app

When a folder named "Portable Settings" exists in same folder as
WebTorrent.exe, then use it instead of the default application config
path.

Closes #358

* packager: remove redundant signing warning

* cross platform zip function

* Set config file path to match config.CONFIG_PATH

* portable app: make electron settings portable

* portable: fix poster/torrent paths

* use cross-zip

* portable app: default download folder inside 'Portable Settings'

README.md

@@ -57,8 +57,16 @@ Where `[platform]` is `darwin`, `linux`, `win32`, or `all` (default).
 
 The following optional arguments are available:
 
-- `--package=[type]` - Package only one output file. `type` is `deb`, `dmg`, `zip`, or `all` (default)
 - `--sign` - Sign the application (OS X, Windows)
+- `--package=[type]` - Package single output type.
+   - `deb` - Debian package
+   - `zip` - Linux zip file
+   - `dmg` - OS X disk image
+   - `exe` - Windows installer
+   - `portable` - Windows portable app
+   - `all` - All platforms (default)
+
+Note: Even with the `--package` option, the auto-update files (.nupkg for Windows, *-darwin.zip for OS X) will always be produced.
 
 #### Windows build notes