implemented new work-stealing scheduler
fixed config script for user-defined build dir
acquire larger stack for context-switching actors

the cs_thread implementation previously used the minimum stack
size possible, which lead to stack overflows in the context-switching
actors when compiled with debugging and logging
use smart pointer to store result of demangling
fixed memory handling of scheduled actors
fixed handling of wr events during MM shutdown
added CPPA_VERSION to config.hpp header
don't enable debug mode per default with logging
removed unused variable
properly spawn new actors in same worker as parent
scheduler fine-tuning + logging improvements

the scheduler no longer runs event-based actors after spawning them
without any message in their mailbox;
this patch also improves logging in the scheduler implementation
to give better insights into the work-stealing workflow
streamlined init & shutdown of scheduler
Merge branch 'master' into unstable
moved assignment of last_worker into crit. section
use atomic head/tail pointer in prod/consumer list

this patch makes the head and tail pointer of
util::producer_consumer_list atomic in order to have
a thread-safe implementation of the empty() member function
maintenance

Firstly, this patch resolved some minor issues:

- fixed some minor mistakes in the documentation
- fixed several warnings such as sign conversions, weak vtables, etc.
- got rid of unused enum value `hm_timeout_msg`
- use 64bit integer for duration type, closes #9
- throw exception when trying to use a negative timeout for receiving messages

Secondly, this patch enforces a better and more C++11-ish coding style:

- use `noexcept` instead of `throw()`
- annotate fallthroughs in switch statements via `CPPA_ANNOTATE_FALLTHROUGH`
- prefer `enum class` over `enum`
- prefer exhaustive list of cases over relying on a `default:` case
- suppress third party warnings via `CPPA_PUSH_WARNINGS`/`CPPA_POP_WARNINGS`
- use `[[noreturn]]` whenever possible
Merge branch 'master' into unstable
fixed nasty bug in cooperative scheduling policy
support Boost >= 1.54 only and use Boost.Lockfree

this patch adds the config option "--standalone-build" that disables
Boost integration (by defining `CPPA_STANDALONE_BUILD`) and uses
the Boost.Lockfree queue as job list if compiled with Boost support
enum filter_result => enum class msg_type