Start moving documents in Japanese in .h to doc/source/

doc/files.am

@@ -336,6 +336,7 @@ absolute_source_files = \
 	$(top_srcdir)/doc/source/rdoc.py \
 	$(top_srcdir)/doc/source/reference.txt \
 	$(top_srcdir)/doc/source/reference/api.txt \
+	$(top_srcdir)/doc/source/reference/api/grn_ctx.txt \
 	$(top_srcdir)/doc/source/reference/api/grn_expr.txt \
 	$(top_srcdir)/doc/source/reference/cast.txt \
 	$(top_srcdir)/doc/source/reference/command.txt \
@@ -784,6 +785,7 @@ source_files_relative_from_doc_dir = \
 	source/rdoc.py \
 	source/reference.txt \
 	source/reference/api.txt \
+	source/reference/api/grn_ctx.txt \
 	source/reference/api/grn_expr.txt \
 	source/reference/cast.txt \
 	source/reference/command.txt \

doc/source/reference/api.txt

@@ -5,4 +5,11 @@
 API
 ===
 
-TODO...
+Groonga can be used as a fulltext search library. This section
+describes APIs that are provided by groonga.
+
+.. toctree::
+   :maxdepth: 1
+   :glob:
+
+   api/*

doc/source/reference/api/grn_ctx.txt

@@ -0,0 +1,49 @@
+.. -*- rst -*-
+
+.. highlightlang:: none
+
+``grn_ctx``
+===========
+
+Summary
+-------
+
+:c:type:`grn_ctx` is the most important object. :c:type:`grn_ctx`
+keeps the current infomation such as:
+
+* The last occurred error.
+* The current encoding.
+* The default thresholds. (e.g. :ref:`match-escalation-threshold`)
+* The default command version. (See :doc:`/reference/command/command_version`)
+
+:c:type:`grn_ctx` provides platform features such as:
+
+* Memory management.
+* Logging.
+
+Most APIs receive :c:type:`grn_ctx` as the first argument.
+
+You can't use the same :c:type:`grn_ctx` from two or more threads. You
+need to create a :c:type:`grn_ctx` for a thread. You can use two or
+more :c:type:`grn_ctx` in a thread but it is not needed for usual
+use-case.
+
+Example
+-------
+
+TODO...
+
+Reference
+---------
+
+.. c:type:: grn_ctx
+
+   TODO...
+
+.. c:function:: grn_rc grn_ctx_init(grn_ctx *ctx, int flags)
+
+   ctxを初期化します。
+
+   :param ctx: 初期化するctx構造体へのポインタを指定します。
+   :param flags: 初期化する ``ctx`` のオプションを指定します。
+   :return: ``GRN_SUCCESS`` on success, not ``GRN_SUCCESS`` on error.

include/groonga.h

@@ -215,14 +215,6 @@ struct _grn_ctx {
 
 #define GRN_CTX_USER_DATA(ctx) (&((ctx)->user_data))
 
-/**
- * grn_ctx_init:
- * @ctx: 初期化するctx構造体へのポインタを指定します。
- * @flags: 初期化するctxのオプションを指定します。
- *
- * ctxを初期化します。
- **/
-
 #define GRN_CTX_USE_QL                 (0x03)
 #define GRN_CTX_BATCH_MODE             (0x04)
 #define GRN_CTX_PER_DB                 (0x08)