Added is_integer() method to integer class
Added alias function is_integer() in rational.pyx
Added is_integer() function to QQbar.py
Added is_integer() function to check if its an integer,in real_double.pyx
Added is_integer() function to complex_double.pyx
Added is_integer() function to complex_number.pyx
Added is_integer() function to Real Number class
Made changes in element.pyx to pass the doc-test.
Removed is_integer() method explicitly and added alias function in rational.pyx
Made formatting changes
FiniteStateMachine: add failing doctests: non-hashable colors

The following behaviour is undesired (docstrings says that
colors are tuples of the colors of the constituent states,
but this is not the case and leads to problems in
Automaton.determinisation):

    sage: A = Automaton([[0, 0, 0]], initial_states=[0])
    sage: B = A.product_FiniteStateMachine(A,
    ....:                                  lambda t1, t2: (0, None))
    sage: B.states()[0].color
    [None, None]
    sage: B.determinisation()
    Traceback (most recent call last):
    ...
    TypeError: unhashable type: 'list'

    sage: A = Automaton([[0, 0, 0]], initial_states=[0])
    sage: B = A.composition(A, algorithm='explorative')
    sage: B.states()[0].color
    [None, None]
    sage: B.determinisation()
    Traceback (most recent call last):
    ...
    TypeError: unhashable type: 'list'

Inserted doctests documenting this undesired behaviour.
FiniteStateMachine.product_FiniteStateMachine, composition: fix unhashable colors

This fixes the failing doctests introduced in commit
2d43fdda50bd5bad3b079e7861fbb725471d1d04.
Automaton.determinisation(): docstring on hashable colors

When Automaton.determinisation() is to be called, colors have to be hashable.
This is now documented both in FSMState and in Automaton.determinisation.
FiniteStateMachine.induced_sub_finite_state_machine: new method

New method to construct a sub-finite-state-machine of the finite
state machine induced by some given states.
Merge #15849 into 'fsm/final_components'
FiniteStateMachine.final_components: New method

Introduced a new method final_components: a final component of a
transducer T is a strongly connected componen C such that there are no
transitions of T leaving C.

Those are the only parts of a transducer which influence the main
terms of the asympotic behaviour of the sum of output labels of a
transducer.
FiniteStateMachine.final_components: another Doctest
fixed error message in induced_sub_finite_state_machine
FiniteStateMachine.induced_sub_finite_state_machine: Removed obsolete remark from docstring
fixed docstring formatting
FiniteStateMachine.final_components: Link [HKW2014] -> arxiv:1404.3680