Add support for SNI

[fitbeast]

Seems like SNI is getting more popular, but the loopj async http lib used in the sdk does not support SNI yet. The square/okhttp project looks like it supports SNI and has an async interface. It also attempts to implement the apache httpclient interface. Any chance that support for this can be added easily? Perhaps drop it in as a replacement for loopj or the apache http lib?

[bajtos]

Related: android-async-http/android-async-http#224 and android-async-http/android-async-http#242

I don't have a strong opinion on this. What I know is that we don't have bandwidth to implement this on our own. If you have time to contribute SNI, then I think adding SNI support to android-async-http is a better use of the time than reworking this SDK to use a different HTTP client.