Introduce start-thread as an entry point so specialized taskmasters
can wrap bindings and condition handlers around hunchentoot new thread thunks.
document START-THREAD and MULTI-THREADED-TASKMASTER.
Further cleanups of the documentation.
Specialize the taskmaster argument in start-thread, lose the declare ignorable.
update changelog
bump version
update html documentation
release 1.2.17
Merge branch 'master', remote branch 'github/edicl/master'