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, 93 insertions, 0 deletions

diff --git a/doc/docs/plugins.rst b/doc/docs/plugins.rst
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+================
+Register Plugins
+================
+
+If you want to extend Pygments without hacking the sources, but want to
+use the lexer/formatter/style/filter lookup functions (`lexers.get_lexer_by_name`
+et al.), you can use `setuptools`_ entrypoints to add new lexers, formatters
+or styles as if they were in the Pygments core.
+
+.. _setuptools: http://peak.telecommunity.com/DevCenter/setuptools
+
+That means you can use your highlighter modules with the `pygmentize` script,
+which relies on the mentioned functions.
+
+
+Entrypoints
+===========
+
+Here is a list of setuptools entrypoints that Pygments understands:
+
+`pygments.lexers`
+
+    This entrypoint is used for adding new lexers to the Pygments core.
+    The name of the entrypoint values doesn't really matter, Pygments extracts
+    required metadata from the class definition:
+
+    .. sourcecode:: ini
+
+        [pygments.lexers]
+        yourlexer = yourmodule:YourLexer
+
+    Note that you have to define ``name``, ``aliases`` and ``filename``
+    attributes so that you can use the highlighter from the command line:
+
+    .. sourcecode:: python
+
+        class YourLexer(...):
+            name = 'Name Of Your Lexer'
+            aliases = ['alias']
+            filenames = ['*.ext']
+
+
+`pygments.formatters`
+
+    You can use this entrypoint to add new formatters to Pygments. The
+    name of an entrypoint item is the name of the formatter. If you
+    prefix the name with a slash it's used as a filename pattern:
+
+    .. sourcecode:: ini
+
+        [pygments.formatters]
+        yourformatter = yourmodule:YourFormatter
+        /.ext = yourmodule:YourFormatter
+
+
+`pygments.styles`
+
+    To add a new style you can use this entrypoint. The name of the entrypoint
+    is the name of the style:
+
+    .. sourcecode:: ini
+
+        [pygments.styles]
+        yourstyle = yourmodule:YourStyle
+
+
+`pygments.filters`
+
+    Use this entrypoint to register a new filter. The name of the
+    entrypoint is the name of the filter:
+
+    .. sourcecode:: ini
+
+        [pygments.filters]
+        yourfilter = yourmodule:YourFilter
+
+
+How To Use Entrypoints
+======================
+
+This documentation doesn't explain how to use those entrypoints because this is
+covered in the `setuptools documentation`_. That page should cover everything
+you need to write a plugin.
+
+.. _setuptools documentation: http://peak.telecommunity.com/DevCenter/setuptools
+
+
+Extending The Core
+==================
+
+If you have written a Pygments plugin that is open source, please inform us
+about that. There is a high chance that we'll add it to the Pygments
+distribution.