doc: add create index docs

Author: Christian Hergert

doc/mongoc_collection_create_index.txt

@@ -0,0 +1 @@
+mongoc_collection_ensure_index.txt

doc/mongoc_collection_ensure_index.txt

@@ -4,13 +4,19 @@ mongoc_collection_ensure_index(3)
 
 NAME
 ----
-mongoc_collection_ensure_index - Vivify an index on a collection
+mongoc_collection_create_index, mongoc_collection_ensure_index - Vivify an index on a collection
 
 
 SYNOPSIS
 --------
 [source,c]
 -----------------------
+bool
+mongoc_collection_create_index (mongoc_collection_t      *collection,
+                                const bson_t             *keys,
+                                const mongoc_index_opt_t *opt,
+                                bson_error_t             *error);
+
 bool
 mongoc_collection_ensure_index (mongoc_collection_t      *collection,
                                 const bson_t             *keys,
@@ -21,6 +27,26 @@ mongoc_collection_ensure_index (mongoc_collection_t      *collection,
 
 DESCRIPTION
 -----------
+
+mongoc_collection_create_index
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The _mongoc_collection_create_index()_ function will request the creation of
+a new index.
+
+This function will use the _createIndexes_ command if available on the
+MongoDB server. If not, it will fallback to inserting into system.indexes
+for compatibility with MongoDB <= 2.4.
+
+See linkmongoc:mongoc_index_opt[7] for options on creating indexes.
+
+
+mongoc_collection_ensure_index
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This function is deprecated and should not be used in new code. Use
+_mongoc_collection_create_index()_ instead.
+
 The _mongoc_collection_ensure_index()_ function requests that an index on
 'collection' be created if one does not already exist.