remove a bunch of old task apis. update test_task to new api.
Much smarter stack cache, with larger defaults.  Makes stack_allocator a namespace.
control init ordering for set_default_stacksize()
store signal stack addr so valgrind doesn't think it's leaked
Merge pull request #66 from chipdude/chip/stacks

Much smarter stack cache, with larger defaults.
Merge branch 'master' of github.com:toffaletti/libten
correct iterator usage
go back to count based max for stack cache
register signal stack with valgrind
fix hang on parse_arg, like --help
re-add cache_maxsize
allow setting default stacksize once via task::main
simplify stack cache logic
boost unit test isn't thread safe. don't use it from threads.
add task::join and task::joinable