Splits the progress @echo statements in the Makefile.
Replaces some @echo recipes by @printf.

The echo command does not understand the -n argument on Mac OS X.
This is due to the fact that:

  - Makefile calls /bin/sh to execute a command
  - in Mac OS X, /bin/sh is a link to bash
  - in Mac OS X, bash is compiled with --enable-strict-posix-default

Therefore, the echo command does not have the -n argument.

printf on the other hand is a builtin function that works well on Mac OS X and Linux.
Moves one @printf statement to be more accurate.
Modifies the Makefile to use local npm install **when available**

The change introduced in 5bd8cdca9 was:

  - partial, as not all the command were translated
  - preventing the use of a global npm installation
Allows the user to set different source and destination in Makefile.

A user can use the following command to determine where to copy the resulting css file:

    $ BOOTSTRAP=<my-path> make
Changes some more commands to use the local npm install.
Added retina image support mixin
Fix typo on JavaScript documentation
Merge pull request #6944 from canburak/3.0.0-wip

Fixed typo on JavaScript documentation
restore jekyll-based css.html to docs
fix #6950: use var for font-family
Update gallery examples on homepage; make all gallery entries open in new tabs
twerk gallery examples to stay at 400px or less for proper retinafying
Don't affix the fixed navbars in mobile views
More accurate padding for fixed navbars at >768px
Overhaul carousel a bit more:

* Drop custom type arrow controls for glyphicons icons instead for more consistent rendering
* Remove the captions and instead let folks implement what they want in the carousel
* Move the indicators to the bottom middle instead of top right
* Lighten up gradients on the edges for less harsh lighting
All Glyphicons now require a base class, e.g. .glyphicon.glyphicon-star
Nuke @mdo's photos from the repo since we're using holder.js for carousel demo
Nuke the old_docs.css file
Nuke the fluid example since it's no longer applicable