Add support for Content-Length in background_fetch config
update CHANGES for TS-2683
TS-2683: build fix
TS-2729: add missing error constant
Fix build problem for CentOS, Ubuntu
Tidy up background_fetch includes
Fix release date
TS-3171: minor style updates to Tokenizer

Make some minor style tweaks to Tokenizer so that it is a little
more conventional and easier to use. Rewrite the regression test
so it tests something.
TS-1432: Adding TSMutexDestroy to API
TS-1432: Update changes