Specify bundles to build with RuntimePlatform #5
Description
AssetBundleBuilder.BuildAssetBundles() allows the user to specify a BuildTarget to explicitly specify which platform to build a bundle for. To a degree this makes sense, since Unity's underlying build API also takes a BuildTarget as a parameter, however it's inconsistent with how we try to use RuntimePlatform everywhere else.
As part of the design of asset-bundle-builder, I decided to standardize around RuntimePlatform instead of BuildTarget because RuntimePlatform more accurately reflects what platform a built asset bundle supports. To avoid confusion and keep the API consistent, we should remove all usage of BuildTarget from the public API and replace it with RuntimePlatform. We can always determine what build target to use from the runtime platform, and that can be kept as an implementation detail that doesn't need to be exposed to the user.