Release 2.6.0

• Add struct _u_request->callback_position to know the position of the current callback in the callback list
• Use MHD_USE_AUTO instead of MHD_USE_THREAD_PER_CONNECTION if libmicrohttpd is newer then 0.9.52
• Add network_type in struct _u_instance and struct _u_request to specify IPV4, IPV6 or both networks
• Add check_server_certificate_flag, check_proxy_certificate, check_proxy_certificate_flag and ca_path in struct _u_request to add more precision and control on SSL verification in u_send_request
• Add functions ulfius_set_string_body_request, ulfius_set_binary_body_request, ulfius_set_empty_body_request
• Add url_path in struct _u_request to store the url path only, without query parameters
• Add ulfius_url_decode and ulfius_url_encode
• Clean code, add more tests
• Install pkgconfig file when using Makefile
• Fix #121 where websockets messages of 126 or 127 bytes long made errors
• Use gnutls_rnd() instead of rand()
• Fix sneaky bug where endpoint injection inside a endpoint callback can lead to wrong callback calls, or even worse, crashes