Improve the speed of evbuffer_readln() This makes some cases of bench_http about 5% faster. Our internal evbuffer_strpbrk() function was overly general (it tried to handle all character sets when we only used it for "\r\n"), and not very efficient (it called memchr once for each character in the buffer until it found a \r or a \n). It actually showed up in some profiles for HTTP testing, since evbuffer_readln() calls it when doing loose CRLF detection. This patch replaces it with a faster implementation.