Gettin' on the Gulp-train

Setup build environments with CLI arguments.
  - default to 'development'
  - pass `--env [p|prod|production]` for 'production' mode

Styles
  - compile SCSS
  - concat into single file
  - autoprefixer
  - minify (CSSO, in 'production' only)
  - remove unused styles

Scripts
  - JSHint
  - concat into single file
  - uglify (in 'production' only)

Images
  - minify

HTML
  - copy to build/
  - minify (in 'production' only)