Add blueprint descriptions to ember help generate

Also display '(overridden)' next to overridden blueprints.

Addresses #1237
Addresses #1274

Pass options through printBasicHelp & printDetailedHelp

Hide overridden blueprints unless verbose flag is set

Add example descriptions to built-in blueprints

Add availableOptions to Blueprint
Removed broccoli-sweetjs from registry since it doesn't work.

If you try and use it, you'll simply get `Unknown statement type: ImportDeclaration` because sweetjs doesn't know about ES6 modules yet.
Merge pull request #1279 from jgwhite/blueprint-list-description-and-overrides

Add blueprint descriptions to ember help generate
Ensure that `isType` matches if the extension is the type.
Merge pull request #2014 from rwjblue/remove-sweet

Remove broccoli-sweetjs from registry.
[windows] - always split diff using unix line endings

jsdiff always uses unix line endings `\n` which causes tests to fail on
windows because we are trying to split the result based on enviornment EOL
Merge pull request #2015 from raytiley/diff-line-endings

[windows] - always split diff using unix line endings