Add support to logarithms with different bases

[AziAdFH]

Is it possible to add support for logarithms with different bases by formula log_a(b) = log(b)/log(a)?
\log _2(10) => (log(10)/log(2))
\log _{2-x}\(\frac{5+2}{x^2}) => (log(\frac{5+2}{x^2})/log(2-x))

P.S. Thanks a lot for the great library!