Retrofit some EmberCPM macros with composable macro support

[mike-north]

• among - This should be able to see if a given value is among a set of literals and properties (instead of just literals)
• fmt - Should allow combining of properties and literals. Could be very useful in conjunction with a concat macro, for example.
• join - Should allow joining of literals mixed with properties

I'll be sending along PRs for these, one by one

[mike-north]

removed notAmong from the list due to #82 #76

[mike-north]

All three of these will require Ember.literal or some analogous concept.