added elementary arithmetic operations on algebraic numbers
fixed bug in ``minpoly_pow``; added ``minpoly_neg``
faster ``minpoly_pow`` using resultants
faster ``minpoly_op_algebraic_number`` with co-prime degrees
added option ``compose`` to ``minpoly`` to use ``minpoly1``

``minpoly1`` computes the minimal polynomial using arithmetic operations
on minimal polynomials.

Added ``minpoly_add``, ``munpoly_mul``.

Added ``_minpoly_sin``, ``_minpoly_cos`` and ``_minpoly_exp`` to
compute the minimal polynomial of trigonometric expressions.
This implementation is incomplete;
the case with angles ``pi*p/q`` with ``q`` prime has been implemented.
``minpoly`` now uses by default ``minpoly1``
``minpoly1`` can deal with ``RootOf`` objects

added default maximum precision to ``_choose_factor``
covered more cases in ``_minpoly_ex``

taken away ``op='div'`` in ``minpoly_op_algebraic_number``
``minpoly_op_algebraic_number`` only with resultant method
fixed bug in _minpoly_mul
fixed bug in ``_minpoly_pow`` in case of division by zero
In ``minimal_polynomial`` changed docstring and eliminated ``prec`` option

with ``compose=True`` used ``primitive`` always

Changed ``minpoly1`` to ``_minpoly1``
Changed ``minpoly_op_algebraic_number`` to ``_minpoly_op_algebraic_number``

eliminated ``has_algebraic_number``
small optimizations in ``_minpoly_op_algebraic_number`` and ``_minpoly_pow``
fixed bug in ``_nthroot_solve``
fixed bug in ``_separate_sq``; improved coverage
added test, which is skipped because it hangs.
Added argument for irreducibility in ``_minpoly_op_algebraic_number``
improved ``_minpoly_sin``; modified ``_minpoly_cos``
eliminated useless code in `` _minpoly_cos``
Fixed bug in ``_minpoly_op_algebraic_number``, added test for it;
thanks to Katja Sophie Hotz for both.