Builds manifest

[sveetch]

Is your feature request related to a problem? Please describe.
Purpose of this feature would be to create a JSON file of built files from a compilation alike webpack-bundle-tracker does for Webpack.

Describe the solution you'd like
Every time a compilation is performed, the compiler should write a file like boussole-stats.json into the target directory (as defined from settings) which would list every built CSS file item.

File item may contains some information like the main Sass source (as a relative path from source dir) it comes from, the filename, maybe the file size, its relative (to the target dir) path and possibly the absolute file path.

Additional context

It would help developer to integrate CSS built assets into their project with a little bit of code into an asset manager.

Also since the new feature HASH_SUFFIX, the built filenames can change on every compile. file.scss won't render just to file.css but to file.3f91ee4f01a2081b6127.css, then file.18e67c22d578d32b07e3.css, etc..

It can not be simply included anymore with file.css, this manifest would help to include it without to modify template each time a compile has been done.