all: fix CPack directives

The binaries are now built into "buildvle" directory. This directory is
now ignored when packaging.
muParser: fix the name of the CMake project

The name of the project now matches the name of the pkg.
decision: fix the data directory management

A new port parameter is generated by the modeling plugin. the
PackageName parameter tell where to load the plan file.
(closes #51)
package-1.1.0-beta2
ChangeLog: removed

We remove ChangeLog from repository.
README: switch to rst
README: add ext.muparser and vle.forrester

The repository have now ext.muparser and vle.forrester packages.
README: update
decision: fix the plugin selection management

The member data structure of the drawing area dedicated to the
selection where not reset when the modeling plugin were reuse inisde a
gvle session.
(closes #55)