Characteristic function

[simonbyrne]

Add a function which gives the characteristic function for each distribution. This would make it easier to implement the fft-based kde (#29 and #31) for different kernels.

I don't know what the best name would be: characteristic, charfun, cf?

[johnmyleswhite]

I like characteristic. But I think someone started implementing this as cf.

[jiahao]

characteristic is potentially ambiguous since characteristic something is ubiquitous in mathematics. But I'm open to changing from cf.

[johnmyleswhite]

I'm working on this right now using mgf and cf. If people want to change the names at some point in the future, I'm open to it.

[johnmyleswhite]

Enough distributions have this functionality now that I'm going to close this issue. Please open specific issues for adding mgf and cf for specific distributions.