Add ISOP expression printing to print.hpp

[brainkz]

SOP expressions are useful when constructing the GENLIB library for technology mapping. The functions print_sop_expression and to_sop_expression convert the complete truth table and produce the SOP expression, e.g., (b&c)|(a&c)|(a&b) for majority-3.

[msoeken]

Thanks for the contribution. I left some small comments that should be addressed before merging.

[msoeken]

This change should be reverted, as we expect an empty line at the end of every file.

[msoeken]

In the formatting for this library we expect spaces after opening and before closing parentheses.

[brainkz]

Updated my pull request according to the requested changes:

• No brackets around RHS
  bool brackets = __builtin_popcount( mask ) > 1;

• Run clang-format to correct formatting, particularly:
  void print_sop_expression( TT tt, std::ostream& os = std::cout )
for ( auto cube : cubes )
if ( !first_cube )

• Removed empty line before include

#include "algorithm.hpp"
#include "karnaugh_map.hpp"
#include "operations.hpp"
#include "constructors.hpp"
#include "isop.hpp"

• Reverted changes in print.cpp