Embed bindata optionally

[tboerger]

I would like to embed the bindata optionally based on a build tag, since we are running a Go application I really love the feature to server everything from the single file.

[bkcsoft]

Cannot up-vote this issue enough, this is killing my dev-speed because I have to recompile all the time for things that aren't even being compiled 😒

[bkcsoft]

Maybe add a pre-compile-tag as well while we're at it, which pulls in templates/, scripts/, public/ for a truly single-binary release 😉

[strk]

My PR #78 is solely about the optionality of embedding