snippet: Add some more documentation

This adds a documentation section for CoglSnippet which gives an
overview of how to use them. It also fixes some syntax errors in the
existing documentation and adds the missing pipeline functions for
adding snippets to the documentation sections file.

Reviewed-by: Robert Bragg <robert@linux.intel.com>

doc/reference/cogl-2.0-experimental/Makefile.am

@@ -89,6 +89,7 @@ IGNORE_HFILES=\
 	cogl-program.h				\
 	cogl-shader-private.h			\
 	cogl-shader.h				\
+	cogl-snippet-private.h			\
 	cogl-sub-texture-private.h		\
 	cogl-texture-2d-private.h		\
 	cogl-texture-2d-sliced-private.h	\

doc/reference/cogl-2.0-experimental/cogl-2.0-experimental-docs.xml.in

@@ -67,6 +67,7 @@
       <title>Setting Up A GPU Pipeline</title>
       <xi:include href="blend-strings.xml"/>
       <xi:include href="xml/cogl-pipeline.xml"/>
+      <xi:include href="xml/cogl-snippet.xml"/>
     </section>
 
     <section id="cogl-buffer-apis">

doc/reference/cogl-2.0-experimental/cogl-2.0-experimental-sections.txt

@@ -237,6 +237,24 @@ cogl_rectangles_with_texture_coords
 cogl_rectangle_with_multitexture_coords
 </SECTION>
 
+<SECTION>
+<FILE>cogl-snippet</FILE>
+<TITLE>Shader snippets</TITLE>
+CoglSnippet
+CoglSnippetHook
+cogl_snippet_new
+cogl_snippet_get_hook
+cogl_is_snippet
+cogl_snippet_set_declarations
+cogl_snippet_get_declarations
+cogl_snippet_set_pre
+cogl_snippet_get_pre
+cogl_snippet_set_replace
+cogl_snippet_get_replace
+cogl_snippet_set_post
+cogl_snippet_get_post
+</SECTION>
+
 <SECTION>
 <FILE>cogl-primitives-deprecated</FILE>
 <TITLE>Primitives (Deprecated)</TITLE>
@@ -609,6 +627,9 @@ cogl_pipeline_set_uniform_float
 cogl_pipeline_set_uniform_int
 cogl_pipeline_set_uniform_matrix
 
+cogl_pipeline_add_snippet
+cogl_pipeline_add_layer_snippet
+
 <SUBSECTION Private>
 cogl_blend_string_error_get_type
 cogl_blend_string_error_quark