add cmake finder for graphviz dot program and then conditionally comp…

A few binary elementwise ops

fix install directory name. not sure why it worked on osx, but who re…

add cmake finder for graphviz dot program and then conditionally compile visualization based on finding

Finish broadcast type propagation, add tests.

Add eigen support

add eigen as external project.
add very simple eigen unit test to test building/linking

Fix/sanitize type comparisons, add test

* Cleaned up the CMakeLists.txt to properly do the include paths and fixed the install targets.
Also cleaned up the header files located in sub directories.
* Added a simple C++ example with Makefile.
* UPdated the readme with TF usage instructions.

De-use and cleanup op names.

Cyphers/names

topological sort working with unit test

Bob/relax requirements

Disable infinite recursion in ScalarConstant::node_id()

Use direct implementation of is_parameter, is_op