roby version 0.7.2 has been released!

# What is Roby ?

Roby is a plan manager: it allows to represent, execute and adapt a plan, which
is a representation of the past, present and future activities of a robot along
with the information needed to verify that their executin is going well, and to
manage errors.

Roby is:
* a task/event model in which one can represent the activities (Roby::Task) and
the noticeable situations during execution (Roby::EventGenerator,
Roby::Task.event).
* a set of task relations describing the interactions between the activities
(Roby::TaskStructure).
* a set of event relations describing the reaction the system should have in
response to some situations (Roby::EventStructure).
* error management tools which allow to catch errors during execution and
repair them (i.e. let the system manage the error).
* a mean to modify the plan as it is being executed (Roby::Transaction)
* (G)UI tools for interacting/controlling the living system.
* all of that in a multi-robot context.

Changes:

### 0.7.2

* fixed a memory leak regarding the event propagation histories. Until now,
all the propagation histories where kept through Event#sources, leading to
actually keeping most plan objects since the beginning of execution. This
is fixed by internally using weak references. Histories will therefore be
truncated as the Ruby GC removes references to the concerned plan objects.
* misc small fixes, which mostly remove some false negatives in the test suite
* small change to be compatible with 1.8.7