Do not enfore exactly one = in redefiniton

This behaviour currently prohibits redefining options
to complex more values like:

-D "MyTask.extra_opts=PATH=/opt/bin USER=nobody DEBUG=true"
Merge pull request #14 from queria/redef-raw-value

Do not enfore exactly one = in redefiniton
Report details about misconfigured tasks

When dict with task's configuration does not
contains 'task' key, or when the instantiation
of the Task's class failed (wrong arguments for ex),
it's much more helpful to log which task and with which
arguments failed.
Merge pull request #15 from queria/log-misconf

Report details about misconfigured tasks
Merge branch 'devel'
new release