Generalized Bezout numbers and linear-product start systems in PHCv2.

Besides some renaming nothing is new in this release.

Four types of start systems are implemented, based on total degree,
m-homogeneous, multi-homegenous, and generalized Bezout number.

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file name                          : short description
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total_degree_start_systems         : start systems based on total degree
ts_startsys                        : test on total-degree based start systems
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sets_of_unknowns                   : set of unknowns of polynomials
sets_of_unknowns_io                : input/output for sets of unknowns
partitions_of_sets_of_unknowns     : partitions of sets of unknowns
partitions_of_sets_of_unknowns_io  : input/output for partitions
degrees_in_sets_of_unknowns        : compute degrees and degree tables
m_homogeneous_bezout_numbers       : calculation of m-homogeneous bounds
random_product_system              : systems of products of hyperplanes
random_product_system_io           : input/output for product systems
m_homogeneous_start_systems        : creation of m-homogeneous start systems
interpolating_homotopies           : homotopies based on interpolation
interpolating_homotopies_driver    : driver for interpolating homotopies
drivers_for_m_homogenization       : menu-driver for m-homogenization
ts_drivmhom                        : calls the driver for m-homogenization
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generate_unions                    : all unions of k numbers from a range
degree_structure                   : model for multi-homogeneous structure
multi_homogeneous_start_systems    : construct multi-homogeneous start systems
drivers_for_multi_homogenization   : menu-driver for multi-homogenization
ts_drivmuho                        : calls the driver for multi-homogenization
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set_structure                      : model of general degree structure
set_structure_io                   : input/output of set structures
degree_sets_tables                 : generalized permanents
random_product_start_systems       : construct random linear-product systems
drivers_for_set_structures         : menu-driver for set structures
ts_drivss                          : calls the driver for set structures
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wc *adb counts 4286 lines of Ada code