Lock to npm@2.7.5 in AppVeyor

We need this in order work around an issue with npm
https://github.com/npm/npm/issues/8517

Release v3.1.2

Fix multi-file compile only writes to the last path when multiple files import a changed partial

CLI: Adds source-map=directory support

* For multi-file compilation.
* Written test.
* Usage:

  ```javascript
  node-sass --source-map source-map/dir --output css/path style/src/
  ```

Issue URL: #903.
PR URL: #964.

Release v3.1.1

Fix ability to watch whole directory

Bump Libsass to 3.2.4

--help fix: mentioning options also in stdin/stdout syntax

Switch back to official pangyp

We temporarily switched to a fork until
https://github.com/rvagg/pangyp/pull/5 was resolved.

Bump Libsass to 3.2.3

Load am11/pangyp from HTTPS

Update README.md

Libsass now allow us to add the missing compact and expanded output styles.

Remove use of 'package' as a variable name in install.js

Bump 3.0.0

build: Adds win_delay_hook so iojs runs with alias

Before building, first apply the following patch
to pangyp: rvagg/pangyp#5 (until it is merged).

Issue URL: #870.

Improve binary file download error handling

Do not throw exception on invalid/mangled URL
Provide consistent error message with the URL
on all failures.

Watcher should prioritize cwd when resolving imports

Create a troubleshooting guide