revlogio: speed up parsing
- precalcuate ending offset
- pull some variables into local scope
- separate inline and out of line code paths
default = 'changelog'
header = header.tmpl
changelog = changelog.tmpl
changelogentry = changelogentry.tmpl
filelog = filelog.tmpl
filelogentry = filelogentry.tmpl
tags = tags.tmpl
tagentry = tagentry.tmpl