Update of tests and doc

* Updated doc of ware methods
* Updated file format for input data tests
* Updated tests of input data primitives
Add of GNUplot observer for export simulation variables to graphs

* Added export.vars.plot.gnuplot
* Updated tests

(closes OpenFLUID/openfluid#56)
Switch to version 2.0.0~beta1
Clean and update of observers and examples simulators

* Updated version in signatures
* Updated description in signature of GNUplot observer
* Removed obsolete files