gcoap: update the example reference

sys/include/net/gcoap.h

@@ -65,7 +65,7 @@
  * reading the request, the callback must use functions provided by gcoap to
  * format the response, as described below. The callback *must* read the request
  * thoroughly before calling the functions, because the response buffer likely
- * reuses the request buffer. See `examples/gcoap/gcoap_cli.c` for a simple
+ * reuses the request buffer. See `examples/gcoap/client.c` for a simple
  * example of a callback.
  *
  * Here is the expected sequence for a callback function:
@@ -105,7 +105,7 @@
  *
  * Client operation includes two phases: creating and sending a request, and
  * handling the response asynchronously in a client supplied callback. See
- * `examples/gcoap/gcoap_cli.c` for a simple example of sending a request and
+ * `examples/gcoap/client.c` for a simple example of sending a request and
  * reading the response.
  *
  * ### Creating a request ###
@@ -219,7 +219,7 @@
  * identify the slice with a Block2 option. This implementation toggles the
  * actual writing of data as it passes over the code for the full response
  * body. See the _riot_block2_handler() example in
  * [gcoap-block-server](https://github.com/kb2ma/riot-apps/blob/kb2ma-master/gcoap-block-server/gcoap_block.c),
  * which implements the sequence described below.
  *
  * - Use coap_block2_init() to initialize a _slicer_ struct from the Block2
@@ -244,7 +244,7 @@
  * The server must ack each blockwise portion of the response body received
  * from the client by writing a Block1 option in the response. See the
  * _sha256_handler() example in
  * [gcoap-block-server](https://github.com/kb2ma/riot-apps/blob/kb2ma-master/gcoap-block-server/gcoap_block.c),
  * which implements the sequence described below.
  *
  * - Use coap_get_block1() to initialize a block1 struct from the request.
@@ -260,7 +260,7 @@
  *
  * The client requests a specific blockwise payload from the overall body by
  * writing a Block2 option in the request. See _resp_handler() in the
- * [gcoap](https://github.com/RIOT-OS/RIOT/blob/master/examples/gcoap/gcoap_cli.c)
+ * [gcoap](https://github.com/RIOT-OS/RIOT/blob/master/examples/gcoap/client.c)
  * example in the RIOT distribution, which implements the sequence described
  * below.
  *
@@ -284,7 +284,7 @@
  *
  * The client pushes a specific blockwise payload from the overall body to the
  * server by writing a Block1 option in the request. See _do_block_post() in
  * the [gcoap-block-client](https://github.com/kb2ma/riot-apps/blob/kb2ma-master/gcoap-block-client/gcoap_block.c)
  * example, which implements the sequence described below.
  *
  * - For the first request, use coap_block_slicer_init() to initialize a