feat: improve template helper wiring

src/helpers/handlebars-helpers.coffee

@@ -17,23 +17,28 @@ Register useful Handlebars helpers.
 @method registerHelpers
 ###
 
-module.exports = ( theme, opts ) ->
+module.exports = ( theme, rez, opts ) ->
 
   helpers.theme = theme
   helpers.opts = opts
   helpers.type = 'handlebars'
 
+  # Prepare generic helpers for use with Handlebars. We do this by wrapping them
+  # in a Handlebars-aware wrapper which calls the helper internally.
   wrappedHelpers = _.mapObject helpers, ( hVal, hKey ) ->
     if _.isFunction hVal
       return _.wrap hVal, (func) ->
         args = Array.prototype.slice.call arguments
-        args.shift() # lose the 1st element (func)
-        args.pop() # lose the last element (the Handlebars options hash)
-        func.apply @, args
+        args.shift()                  # lose the 1st element (func) [^1]
+        #args.pop()                   # lose the last element (HB options hash)
+        args[ args.length - 1 ] = rez # replace w/ resume object
+        func.apply @, args            # call the generic helper
     hVal
   , @
-
   HANDLEBARS.registerHelper wrappedHelpers
+
+  # Prepare Handlebars-specific helpers - "blockHelpers" is really a misnomer
+  # since any kind of Handlebars-specific helper can live here
   HANDLEBARS.registerHelper blockHelpers
 
   # Register any theme-provided custom helpers...
@@ -64,3 +69,9 @@ module.exports = ( theme, opts ) ->
         inner: ex
         glob: curGlob, exit: true
       return
+
+# [^1]: This little bit of acrobatics ensures that our generic helpers are
+# called as generic helpers, not as Handlebars-specific helpers. This allows
+# them to be used in other templating engines, like Underscore. If you need a
+# Handlebars-specific helper with normal Handlebars context and options, put it
+# in block-helpers.coffee.