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Import adaptagrams commit 0503f7524f as graphics/adaptagrams v. 0.20160901

Adaptagrams is a library of tools and reusable code for adaptive diagramming
applications, for example: drawing tools, automated document and diagram
layout, smart presentation software, graph drawing, chart layout, etc.

Currently, the Adaptagrams repository includes four cross-platform C++
libraries, These libraries are collectively known as cola (Constraint Layout):

 * libvpsc - a solver for the Variable Placement with Separation Constraints
              problem.

 * libcola - a library for constraint graph layout.

 * libavoid - a library providing high-quality object-avoiding polyline and
              orthogonalconnector routing for use in interactive diagram
              editors.

 * libtopology - a library containing extensions to libcola to support topology
                 preserving constraint-based layout.