Make bindings available in conditional expressions

[MaKleSoft]

For the sake of brevity, it would be nice if the bindings done in the bind attribute would be instantly available in any ifexpressions. Like so:

<template bind="{{ user.address.street as street }}" if="{{ street }}>
   {{ street }}
</template>

Similarly

<template bind="{{ user.address }}" if="{{ street }}>
   {{ street }}
</template>

Perhaps the same thing would be useful for repeat expressions.

[jmesserly]

Funny, I suggested the same thing for repeat here: #13 (comment) :)