Add support for partials and path segments for Handlebars.

This introduces support for some missing features to the Handlebars lexer:
Partials and path segments. Partials mostly appeared to work before, but the
`>` in `{{> ... }}` would appear as a syntax error, as could other
components of the partial. This change introduces support for:

* Standard partials: `{{> partialName}}`
* Partials with parameters: `{{> partialName varname="value"}}`
* Ddynamic partials: `{{> (partialFunc)}}`
* Ddynamic partials with lookups: `{{> (lookup ../path "partialName")}}`
* Partial blocks: `{{> @partial-block}}`
* Inline partials: `{{#*inline}}..{{/inline}}`

It also introduces support for path segments, which can reference content in
the current context or in a parent context. For instance, `this.name`,
`this/name`, `./name`, `../name`, `this/name`, etc. These are all now tracked
as variables.

1 files changed, 40 insertions, 0 deletions

diff --git a/tests/test_using_api.py b/tests/test_using_api.py
new file mode 100644
index 00000000..16d865e6
--- /dev/null
+++ b/tests/test_using_api.py
@@ -0,0 +1,40 @@
+# -*- coding: utf-8 -*-
+"""
+    Pygments tests for using()
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    :copyright: Copyright 2006-2015 by the Pygments team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+
+import unittest
+
+from pygments.lexer import using, bygroups, this, RegexLexer
+from pygments.token import String, Text, Keyword
+
+class TestLexer(RegexLexer):
+    tokens = {
+        'root': [
+            (r'#.*',
+             using(this, state='invalid')),
+            (r'(")(.+?)(")',
+             bygroups(String, using(this, state='string'), String)),
+            (r'[^"]+', Text),
+        ],
+        'string': [
+            (r'.+', Keyword),
+        ],
+    }
+
+
+class UsingStateTest(unittest.TestCase):
+    def test_basic(self):
+        expected = [(Text, 'a'), (String, '"'), (Keyword, 'bcd'),
+                    (String, '"'), (Text, 'e\n')]
+        t = list(TestLexer().get_tokens('a"bcd"e'))
+        self.assertEqual(t, expected)
+
+    def test_error(self):
+        def gen():
+            return list(TestLexer().get_tokens('#a'))
+        self.assertRaises(KeyError, gen)