Refactor Mongoose documentation

docs/c-api/coap.h/intro.md

docs/c-api/dns.h/intro.md

docs/c-api/dns_server.h/intro.md

docs/c-api/dns_server.h/mg_dns_create_reply.md

docs/c-api/dns_server.h/mg_dns_reply_record.md

docs/c-api/dns_server.h/mg_dns_send_reply.md

docs/c-api/http.h/intro.md

docs/c-api/http.h/mg_url_decode.md

docs/c-api/http_client.h/intro.md

docs/c-api/http_client.h/mg_connect_http.md

docs/c-api/http_client.h/mg_connect_http_opt.md

.../c-api/http_client.h/mg_http_create_digest_auth_header.md

docs/c-api/http_server.h/intro.md

docs/c-api/http_server.h/mg_file_upload_handler.md

docs/c-api/http_server.h/mg_fu_fname_fn.md

docs/c-api/http_server.h/mg_get_http_header.md

docs/c-api/http_server.h/mg_get_http_var.md

docs/c-api/http_server.h/mg_http_check_digest_auth.md

docs/c-api/http_server.h/mg_http_parse_header.md

docs/c-api/http_server.h/mg_http_serve_file.md