Format output print

[mrx23dot]

Printing output should be human readable:

model = system_identification()
print(model)

and model specific,

e.g. ARMAX with IC=None output should look something like:

print(f'''
  G	{m.G},
  H	{m.H},
  na	{m.na},
  nb	{m.nb},
  nc	{m.nc},
  nd	{m.nd},
  nf	{m.nf},
  theta	{m.theta},
  ts	{m.ts},
  Vn	{m.Vn},
  NUMERATOR	{m.NUMERATOR},
  NUMERATOR_H	{m.NUMERATOR_H},
  DENOMINATOR	{m.DENOMINATOR},
  DENOMINATOR_H	{m.DENOMINATOR_H},
  Yid	{m.Yid}
''')

maybe an equation in picture too?

[mrx23dot]

Also Table 8.1 documentation is wrong:

AttributeError: 'ARMAX_MIMO_model' object has no attribute 'nd'. 
AttributeError: 'ARMAX_MIMO_model' object has no attribute 'nf'.