Eq2RV

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   Converts equinoctial elements to r and v for an elliptic orbit.
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   Form:
   [r, v] = Eq2RV( eq, tol, mu )
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   Inputs
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   eq              (6,:) Elements vector [a,P1,P2,Q1,Q2,l]
   tol                   Tolerance for Kepler's equation solver
   mu                    Gravitational constant

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   Outputs
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   r               (3,1) position vector
   v               (3,1) velocity vector

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   References:   Battin, R.H., An Introduction to the Methods and Mathematics
                 of Astrodynamics, AIAA, New York, 1987, pp. 493-494.
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