directly handle white space and support multiline tags

test/corpus/load.txt

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+==================
+Load Single Library
+==================
+
+{% load static %}
+
+---
+
+(template
+  (content)
+  (load
+    (library
+      (identifier)))
+  (content))
+
+==================
+Load Multiple Libraries
+==================
+
+{% load i18n static %}
+
+---
+
+(template
+  (content)
+  (load
+    (library
+      (identifier))
+    (library
+      (identifier)))
+  (content))
+
+==================
+Load Dotted Library
+==================
+
+{% load django.contrib %}
+
+---
+
+(template
+  (content)
+  (load
+    (library
+      (identifier)
+      (identifier)))
+  (content))
+
+==================
+Load Names From Library
+==================
+
+{% load humanize naturaltime from django %}
+
+---
+
+(template
+  (content)
+  (load
+    (identifier)
+    (identifier)
+    (library
+      (identifier)))
+  (content))