Properly localise transforms/modifiers

Previously, transforms and modifiers were being applied
all the way down the dependency tree. This can lead to
unexpected results, so taking the approach of browserify
where each module may specify these in the package.json
file, e.g.:

{
  "name": "sheetify-module"
  "sheetify": {
    "modifiers": [
        "sheetify-wrap-selectors"
      , "sheetify-variables"
    ],
    "transforms": [
        "sheetify-sass"
      , "sheetify-less"
    ]
  }
}
WIP: tests, modifier/transform configuration
Properly localise transforms/modifiers

Previously, transforms and modifiers were being applied
all the way down the dependency tree. This can lead to
unexpected results, so taking the approach of browserify
where each module may specify these in the package.json
file, e.g.:

{
  "name": "sheetify-module"
  "sheetify": {
    "modifiers": [
        "sheetify-wrap-selectors"
      , "sheetify-variables"
    ],
    "transforms": [
        "sheetify-sass"
      , "sheetify-less"
    ]
  }
}
Merge branch 'master' into breaking-changes

Conflicts:
	index.js
	package.json
Breaking everything out into separate files, adding tests.

index.js was starting to get pretty unwieldy – will hopefully
make it easier to take bits out and make them separate modules
later if required.

Have also included some tests that were in progress before
the most recent changes to the module.
Update documentation for configuration

Still not fully functional, but good to get a description
written down before going and implementing everything
add style-transform, not yet integrated
Simplifying style-deps

* Removing configuration. Easily replicated with local
  transform files.
* Combining transforms and modifiers into source/text
  transforms. Parsing/reparsing between these types
  is now handled transparently.
update ast-pipeline
remove now uneccesary package.json check
transform fixes
1.0.0