Fix issue #35 by writing FlashEmbeddedAssetPackLoader and integrating hxswfml

Since embedded assets load significantly faster than assets on the filesystem, this fix depends on my commit @d29c102. To start embedding assets into flash projects, set embed_assets: true in flambe.yaml.

I know you suggested resurrecting FlashAssetPackager in #35, but I see no reason to reinvent the wheel, and so bundled the Neko version of hxswfml into the bin directory for use by the build process.

It's actually unnecessary to copy the assets to the build directory if embed_assets is true, but if you don't, you lose the ability to have side by side HTML5 and Flash builds, as is made accessible by the default Flambe html scaffolding, so I've done it anyway for now.