ENH: support Akima 1D interpolation
I went hunting for some low-hanging fruit in the area of missing data and came across #7588. I had to implement it a little differently than krogh, pchip, etc. because there is no convenience function for Akima like there are for the already supported methods.

Once #11445 is merged I can rebase.

ok, can you rebase on master
 if you can do this on master (and not depend on the other branch), we can take it.

pls reopen if you wish to do so
 I was just working with akima and I think that there is an issue.  I've posted a bug report here:   [https://github.com/pandas-dev/pandas/issues/21276](https://github.com/pandas-dev/pandas/issues/21276)