Step one of abstracting package description format
Merge pull request #400 from marler8997/SdlSupport1

Step one of abstracting package description format
More package info abstraction
Merge pull request #401 from marler8997/SdlSupport2

More package info abstraction (PR number 2 for SDL support)
Updated 3 for SDL support
Merge pull request #403 from marler8997/SdlSupport3

Updated 3 for SDL support
Untangle Package and PackageInfo. See #403.
Rename PackageInfo to PackageRecipe and separate representation from JSON code.

See #403.
Fix build error on GDC.
Remove unused import.
Improve documentation in dub.recipe.packagerecipe.
Quick fix compilation with enabled vibe.d dependency and improve backwards compatibility.

Added a packageInfoFilenames property to keep backwards compatibility.
Fix detection of default "views" folder and remove unused type.
Fix compile error.
toJson doesn't return buildTypes
Merge pull request #406 from sinkuu/fix_tojson

buildTypes disapper from dub.json of a fetched package