[doc] Additional figures

Add three figures ad well as a text file that lists them.

doc/figures/FIGURES.t2t

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+List of figures provided with the OwlPS distribution
+
+
+: **Aggregation sequence diagram**
+  This is actually a sequence diagram showing the whole process of
+  positioning, but it is focused on and best suited to illustrate the
+  aggregation process. An ASCII art version is provided in the OwlPS
+  Aggregator manual page (``owlps-aggregatord.t2t``).
+  - File name: ``owlps_sequence_diagram.plant``
+  - Format: [PlantUML http://plantuml.sourceforge.net/]
+  - PNG conversion command (assuming ``plantuml`` is an alias for
+    ``java -jar /path/to/plantuml.jar``):
+``` plantuml -tpng owlps_sequence_diagram.plant
+    PlantUML also allow to generate SVG or EPS (which in turn can be
+    converted to PDF with [Inkscape http://inkscape.org/] or
+    [epstopdf http://ctan.org/pkg/epstopdf], respectively).
+
+: **OwlPS Positioner's input and output facilities**
+  - File name: ``positioner_input_output.dot``
+  - Format: [Graphviz http://www.graphviz.org/]
+  - PDF conversion command:
+``` dot -Tpdf -o positioner_input_output.pdf positioner_input_output.dot
+
+: **OwlPS Positioner's class diagram**
+  - File name: ``positioner_class_diagram.uxf``
+  - Format: [UMLet http://umlet.com/]
+  - PDF conversion command:
+``` umlet -action=convert -format=pdf -filename=positioner_class_diagram.uxf
+
+: **OwlPS Positioner's internal process**
+  - File name: ``positioner_process.dot``
+  - Format: [Graphviz http://www.graphviz.org/]
+  - PDF conversion command:
+``` dot -Tpdf -o positioner_process.pdf positioner_process.dot

doc/figures/owlps_sequence_diagram.plant

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+@startuml
+
+activate Client
+Client -> Listener: positioning request
+
+activate Listener
+Listener ->> Aggregator: request + SS
+
+' Aggregation timeout
+activate Aggregator
+Aggregator -> Aggregator: aggregation timer
+activate Aggregator #DarkSalmon
+Listener -->> Aggregator: request + SS
+note right: added
+Aggregator -> Aggregator: timeout
+deactivate Aggregator
+
+' Transmit the aggregated request
+Aggregator -> Positioner: aggregated request
+activate Positioner
+
+' Keep timeout
+Aggregator -> Aggregator: keep timer
+activate Aggregator #DarkSalmon
+Listener -->> Aggregator: request + SS
+note right: ignored
+deactivate Listener
+Aggregator -> Aggregator: timeout
+deactivate Aggregator
+
+deactivate Aggregator
+
+Positioner -> Client: computed position
+deactivate Positioner
+deactivate Client
+
+@enduml

doc/figures/positioner_input_output.dot

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+digraph positioner_io {
+        layout=dot
+        size="8,4"
+        margin=0
+        ratio=fill
+        rankdir=LR
+        edge [dir=right]
+
+        /* Programs */
+        node [style=filled, shape=box, fillcolor="#9090fa"]
+        positioner [label="OwlPS Positioner"]
+        client [label="OwlPS Client"]
+        udp_http [label="OwlPS UDP-to-HTTP"]
+        socket_adapter [label="EvAAL SocketAdapter", fillcolor="#cccccc"]
+
+        node [shape=ellipse, fillcolor="#7ec0ea"]
+
+        /* Inputs */
+        "CSV file" -> positioner
+        "UDP socket" -> positioner
+
+        /* Outputs */
+        positioner -> "Standard output"
+        csv_file [label="CSV file"]
+        positioner -> csv_file
+        udp_socket [label="UDP socket"]
+        positioner -> udp_socket
+        udp_socket -> client
+        udp_socket -> udp_http
+        tcp_evaal [label="EvAAL TCP socket"]
+        positioner -> tcp_evaal
+        tcp_evaal -> socket_adapter
+}

doc/figures/positioner_process.dot

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+digraph positioning_process {
+        layout=dot
+        size="8,4"
+        margin=0
+        ratio=fill
+        rankdir=LR
+        edge [dir=right]
+
+        node [style=filled]
+
+        node [fillcolor="#ffaaaa"]
+        edge [label=Request, color=red]
+        InputMedium -> Input
+        Input -> InputLogMedium
+
+        node [fillcolor="#ffaaff"]
+        Input -> Positioning
+        Positioning -> PositioningAlgorithm
+
+        node [fillcolor="#aaaaff"]
+        edge [label=Result, color=blue]
+        PositioningAlgorithm -> Positioning
+        Positioning -> Output
+        Output -> OutputStatistics
+        Output -> OutputMedium
+}