* Done to achieve goal of having our #include directives all start
  with `"ngraph/`, like LLVM does.

add naming of tensors and tensor views
add visualization pass
add graph dump pass

* Implemented binops/unops with different return type from args

* Implemented generic bases class for comparison and arith ops, changed current comparison ops to subclass it

* Added a TraitedType for booleans

* Moved arith and comparison ops to separate header files from `op.h`

Start of external function calling support

Add memory layout and liveness passes.

add test framework

stuff wired up

benchmark segfault for 5M nodes. fun

make traverse_nodes not recursive

print timings on benchmark

unit test for pass manager

All tuples are expanded out to their component tensors.

Output: Describes one tensor output of an node
Input: Described one tensor input to a node, including the output supplying the value.

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

* 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.

Element types needed some reorganization to allow literals to know what kind of values to hold.