write a plugin to provide SASS support

[andy-berry-dev]

Write a plugin(s) that bundles and compiles .sass files.

[dchambers]

Here's what I've managed to glean so far:

• The libsass roadmap shows that libsass will progressively achieve feature parity with Ruby Sass through versions 3.2, 3.3 & 3.4.
• LibSass is currently about to release version 3.2.
• LibSass is only a library and is not a program that a user would directly interact with, whereas SassC or node-sass are programs designed for end-users to use.
• Although you might expect node-sass (or more specifically node-sass-binaries) to have binaries for different operating systems, it actually just seems to contain node specific bindings to LibSass, and nothing we could make use of.
• I can't find SassC binaries anywhere, and even worse SassC doesn't seem to work on WIndows, even though LibSass does.
• There is however a sassc-win project that specifically makes SassC work on Windows, and which is even continuously tested using AppVeyor.

So, although it's not perfect, we could therefore manually compile SassC / SassC-Win on the various platforms we support:

• Linux 32-bit
• Linux 64-bit
• Mac 64-bit
• Windows 32-bit
• Windows 64-bit

and upload these binaries into a public Maven repository that we can then make use of.

[dchambers]

We should liaise with @avsmithy before doing any work on this issue since he has a good idea of the way in which SASS will be used, and whether there are any integration considerations that need to be taken into account.