any of the space chars can follow the esi starting tags

only the space char ' ' can follow the esi starting tags such as "<esi:include", "<!--esi" now, we should allow any space char after these tags. the space chars include: ' ', '\t', '\r' and '\n'.

for example, following common usage:
<!--esi
esi bala bala ...
-->
because no space after the "<!--esi", the esi parser will keep these tags which should be removed.