Add mg_ prefix to mongoose sources

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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