Add connectAsServer & connectAsClient which mirror observeBluetoothSocket & observeConnectDevice but return Single.

[vanniktech]

There's only one emission so they should be returning a Single. Decided to deprecate the old ones in order to not make any incompatible changes. If someone still needs an Observable they can use .toObservable() on the new methods if we ever remove the deprecated methods.

[vanniktech]

CI seems to be flaky:

> Could not resolve all files for configuration ':classpath'.
   > Could not find lint-gradle-api.jar (com.android.tools.lint:lint-gradle-api:26.1.2).
     Searched in the following locations:
         https://jcenter.bintray.com/com/android/tools/lint/lint-gradle-api/26.1.2/lint-gradle-api-26.1.2.jar

[IvBaranov]

First of all, thank you for taking your time to review and contribute.
I looked through all PRs and now I am starting to merge. Travis build passed on all of them as well.

[vanniktech]

Cheers. Thanks for the library!

[vanniktech]

Would appreciate a new release with all of the new features.

[IvBaranov]

Sure.
UPD. Release 2.0.3 is up.