Todo list
- Member Chain<Coeff>::
operator< (const Chain<Coeff>&chain2) const  - also compare direction of arrows
 - File Cob.h
 - precompute cobordism algebra to speed up computation
 - File Coefficients.h
 add rational coefficients via library (boost, mpir, etc)
add integer coefficients with certificates for integer overflow free computations
- File Complex.h
 read/write complexes into backup files to be reused for quick computations like closures or conversion from Z to other coefficients
optimize complex and add graphical output for complexes over Z
- Class Complex<BNObj, BNMor, Coeff>
 - add graphical output (tikz and/or svg)
 - Member interactive (const std::string&metadata, std::vector<File>&files)
 - make this function cope with symmetric tangles and behave more gracefully in edge cases; in particular, remove the necessity of default_
number_ of_ lines.  - Class Khr_
curve  handle gradings more gracefully
implement local systems (if necessary)
- File main.cpp
 - clean-up code basis following guidelines https:/
/ github.com/ isocpp/ CppCoreGuidelines  - Page Options
 Detect integer overflows for rational coefficients.
Make this option work for all coefficients (ie add signs from tensor product sign rule).
- Member Tangle::
Tangle (const File&file)  - explain the structure of a file representing a tangle
 - File Tangles.h
 undo extra twisting after clean-up and add optimized output with extra parameter '-o'