Reorganized the Freestyle Python API in a hierarchical package structure.

Both C- and Python-coded API components were rearranged into logical groups.
New Python modules are packaged as follows:

freestyle - Top-level package
freestyle.types - Classes for core data structues (e.g., view map)
freestyle.chainingiterators - Pre-defined chaining iterators
freestyle.functions - Pre-defined 0D and 1D functions
freestyle.predicates - Pre-defined 0D and 1D predicates
freestyle.shaders - Pre-defined stroke shaders
freestyle.utils - Utility functions

The Python modules are installed in scripts/freestyle/modules.  Pre-defined
styles are installed in scripts/freestyle/styles.

To-do: update styles according to the new Freestyle API package structure.

release/scripts/freestyle/styles/split_at_tvertices.py

@@ -0,0 +1,40 @@
+# ##### BEGIN GPL LICENSE BLOCK #####
+#
+#  This program is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU General Public License
+#  as published by the Free Software Foundation; either version 2
+#  of the License, or (at your option) any later version.
+#
+#  This program is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#  GNU General Public License for more details.
+#
+#  You should have received a copy of the GNU General Public License
+#  along with this program; if not, write to the Free Software Foundation,
+#  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+#
+# ##### END GPL LICENSE BLOCK #####
+
+#  Filename : split_at_tvertices.py
+#  Author   : Stephane Grabli
+#  Date     : 04/08/2005
+#  Purpose  : Draws strokes that starts and stops at Tvertices (visible or not)
+
+from freestyle import ChainSilhouetteIterator, ConstantThicknessShader, IncreasingColorShader, \
+    Nature, Operators, QuantitativeInvisibilityUP1D, TextureAssignerShader, TrueUP1D
+from PredicatesU0D import pyVertexNatureUP0D
+from logical_operators import NotUP1D
+
+Operators.select(QuantitativeInvisibilityUP1D(0))
+Operators.bidirectional_chain(ChainSilhouetteIterator(), NotUP1D(QuantitativeInvisibilityUP1D(0)))
+start = pyVertexNatureUP0D(Nature.T_VERTEX)
+## use the same predicate to decide where to start and where to stop
+## the strokes:
+Operators.sequential_split(start, start, 10)
+shaders_list = [
+    ConstantThicknessShader(5),
+    IncreasingColorShader(1, 0, 0, 1, 0, 1, 0, 1),
+    TextureAssignerShader(3),
+    ]
+Operators.create(TrueUP1D(), shaders_list)