Don't launch npm in the PowerShell

Misc. updates

Updates troubleshooting guide.

The issue was fixed by rvagg/pangyp#5 and shipped with pangyp v2.0.

Remove extra ',' in README

There might be issues with running npm under PS,
therefore let's run npm under CMD.

https://github.com/sass/node-sass/issues/996

http://help.appveyor.com/discussions/problems/2347-npm-275prefer-global-warning-causes-failure-command-executed-with-exception#comment_37223989

https://github.com/npm/npm/issues/8517

Effectively reverts: https://github.com/sass/node-sass/pull/995

Correct typeof reference in README

JavaScript's typeof operator returns "string" not "String" for string values and objects

Change "feth" -> "fetch" in extensions.js comment

Release 3.2.0

Bump Libsass to 3.2.5

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