Code: Minor formatting

Install: Fixes download bug 🐛

PR URL: #743.

* Pointed out by @saper via #694.

PR URL: #743.

* Delivers binary name, paths and download URL
  from lib/extensions.js.

* Allows user to set binary name as environment
  variable with `SASS_BINARY_NAME`.
  * Note: this will supersede default name.
* Allows user to set binary name as in package
  file `"nodeSassConfig": { "binary-name": "" }`.
  * Note: this will supersede default name and
    `SASS_BINARY_NAME` environment variable.
* Allows user to set binary name as parameter to
  invoke any node-sass script with
  `--binary-name` flag.
  * Note: this will supersede default name, name
    defined in package `nodeSassConfig` as well
    as the `SASS_BINARY_NAME` environment
    variable.

* This binary name will be used to construct the:
  * Binary path.
  * Binary download URL.
  * Upload URL.

* Allows user to set binary path as environment
  variable with `SASS_BINARY_PATH`.
  * Note: this will supersede default path.
* Allows user to set binary name as in package
  file `"nodeSassConfig": { "binary-path": "" }`.
  * Note: this will supersede default path and
    `SASS_BINARY_PATH` environment variable.
* Allows user to set binary path as parameter to
  invoke any node-sass script with
  `--binary-path` flag.
  * Note: this will supersede default path, path
    as well as the `SASS_BINARY_PATH` environment
    variable.

* This binary path will be used when:
  * Requiring node-sass package.
  * Downloading binary.
  * Uploading binary.

* Wraps all extensions in `process.sass`
  namespace.

Issue URL: #712.
PR URL: #743.

Issue URL: #731.
Pull Request: #732.

* CSS and Map is casted as Buffer from binding.
Advantages:
  * Buffers are super fast.
  * User can write them to file as is.
  * User can forward to response stream as is.
  * User can strigify it as is:
    * `result.css.toString()`
    * `result.map.toString()` or
      `JSON.stringify(result.map)`
* Updates tests and CLI usage accordingly.
* Updates README to reflect the changes.

Issue URL: #711.
PR URL: #729.

Better default values in the README.md file

This improves the option documentation for #672 and adds the default
information gleaned from the `getOptions` functions and their defaults
from the prior README.md

It is already available in CONTRIBUTING.md.

Because vNext would be v3.0.0.

Code: Improvements

* Pass along the original property names to
  binding so we don't have to disown the
  existing ones and add the new ones.
* Although it is a delicate matter:
  //perfectionkills.com/understanding-delete/
  avoiding delete where you can is better for
  JS optimizers IMO.
  (hint: it de-optimizes the whole object to
   change its internal "shape", which means
   delete single property from object literal
   comes with a perf. trade-off)

PR URL: #727.

Removal of option hashed based success and error callbacks

This change removes the object hash success/error callbacks in
favor of node style callbacks. This includes README and test
updates, including the removal of two tests that are now
obsolete.

This also updates the CLI code pathway to use the node style
callback.

BREAKING API CHANGE
This removes the success/error option keys as ways to register
callbacks into node-sass. Instead, a function should be passed as
the second parameter for the asyncronous `render` call. It takes
a standard node signature of `error, callback`.

Package: Removes unused pacakge 'object-assign'

* Also moves cross-spawn under devDependencies.

Repo: Removes .npmignore, configures package.json

Based on fffc0625.

Code: Formats and fixes JSCS warnings

* To avoid validating node_modules directory.

PR URL: #723.

* Removes unused pacakge `shelljs`.
* Fixes package.json validation issue reported
  by WE2013, based on njs package.json schema:

  > *The value property "repository" must be of
   type "Object", but was "sass/node-sass"*

PR URL: #723.

Misc. improvements

* Adds instructions.
* Removes obsolete info.

This is for DRY'ing comments on repeating issues.

* Based on sindresorhus/meow#2.
* Adds alias -v.
* Improves info text; inspired by Less CLI. :)
* Updates readme.

PR URL: #717.

* Removes tests from publishing. #683
  * Uses new strategy to validate binary after
    the download.
  * Moves mocha under dev-dependencies in
    package.json.
* Truncates the forth portion from v8 version
  as discussed in #710.
* Moves pangyp from dev to main dependencies in
  package.json.

Issue URLs: #683 and #710.
PR URL: #717.

API: Retires non-standard image-path option.