absurlreplacer: write replacements directly to the byte buffer
absurlreplacer: write replacements directly to the byte buffer

The extra step isn't needed and this makes the code simpler.

And slightly faster:

benchmark              old ns/op     new ns/op     delta
BenchmarkAbsUrl        19987         17498         -12.45%
BenchmarkXmlAbsUrl     10606         9503          -10.40%

benchmark              old allocs     new allocs     delta
BenchmarkAbsUrl        28             24             -14.29%
BenchmarkXmlAbsUrl     14             12             -14.29%

benchmark              old bytes     new bytes     delta
BenchmarkAbsUrl        3512          3297          -6.12%
BenchmarkXmlAbsUrl     2059          1963          -4.66%

anthonyfok/hugo,badoet/hugo,ffrizzo/hugo,Zenithar/hugo,tischda/hugo,Zenithar/hugo,fedelibre/hugo,halostatue/hugo,kujohn/hugo,derekperkins/hugo,mdhender/hugo,sprig/hugo,tubo028/hugo,coderzh/hugo,ifraixedes/hugo,tatsushid/hugo,abourget/hugo,bogem/hugo,coderzh/hugo,MarkDBlackwell/hugo,derekperkins/hugo,ffrizzo/hugo,gohugoio/hugo,fhergomez/hugo,MarkDBlackwell/hugo,tatsushid/hugo,ifraixedes/hugo,gohugoio/hugo,fedelibre/hugo,bogem/hugo,ryanclarke/hugo,fedelibre/hugo,tjyang/hugo,halostatue/hugo,anthonyfok/hugo,badoet/hugo,jygastaud/hugo,mayah/hugo,bramp/hugo,digitalcraftsman/hugo,soundrussian/hugo,sprig/hugo,tischda/hugo,anthonyfok/hugo,vbatoufflet/hugo,bramp/hugo,ryanclarke/hugo,fedelibre/hugo,digitalcraftsman/hugo,fhergomez/hugo,mdhender/hugo,melo/hugo,melo/hugo,soundrussian/hugo,vbatoufflet/hugo,mitchchn/hugo,tjyang/hugo,tubo028/hugo,mdhender/hugo,kujohn/hugo,abourget/hugo,mdhender/hugo,mitchchn/hugo,jygastaud/hugo,gohugoio/hugo,mayah/hugo