Remove the git fallback

Remove git sub module documentation

Remove the LibSass git submodule

The git submodule is removed as of #1850.

This was added by me in #874 to support node-sass being installed
as a gitish via GitHub rather than the npm registry.

We publish the LibSass src to npm already so it should continue
to work as is.

I can't imagine accepting a PR with a LibSass bump.

It'd be painful to audit. LibSass should be handled by core.

Commit LibSass source directly from the 3.4.3 tag

* Bump LibSass to 3.4.3

* Update sourcemap test fixtures to match new LibSass behaviour

* Bump sass-spec@v3.4.3

Sass spec releases match 1-1 with LibSass releases and need to be
versioned in sync.

Add a platform variant for installing a musl binary

Fix premature exit before the output stream is fully flushed

Drop dependency lodash.isarray

Bump LibSass to 3.4.0

https://github.com/sass/libsass/releases/tag/3.4.0

Update sourceComments documentation in README.md

Use console for logging instead of npmlog

We started using npmlog for install logging in #1786, then went all
out in #1796. npmlog has caused some issues, namely #1805. It doesn't
provided enough value for how troublesome it is.

The problem sparked #1786 was resolved in 5c7fb7f6.

This reverts commit e7ad0cb3.

This reverts commit fa4515d8.

Send npmlog to stdout