Prepare for release 0.7.1

Migrate to Coroutines 1.0.0 (JuulLabs#25)

Per [Coroutines GitHub page]:

> This is a companion version for Kotlin 1.3.0 release.

[Coroutines GitHub page]: https://github.com/Kotlin/kotlinx.coroutines/tree/1.0.0

Throw GattClosed if Gatt is closed during I/O operation (JuulLabs#23)

Typical behavior of `Channel` is to throw a
`ClosedReceiveChannelException` on invocation of `close` if a `receive`
is suspended. This is unfortunately a bit counter intuitive and can
produce misleading stacktraces (i.e. stacktrace will include `close`
invocation but not `receive`).

In order to be more explicit with our exception stacktraces related to
`Channel` cancelation: catching `ClosedReceiveChannelException` and
explicitly throwing `GattClosed` exception (that carries original
`ClosedReceiveChannelException` as it's cause).

May need to revisit this behavior in the future after `receiveOrClosed`
is implemented per Kotlin/kotlinx.coroutines#330.

Add CoroutinesGattDevice and BluetoothDevice extension functions (Juu…

…lLabs#20)

Provides a thread safe mechanism of having a `BluetoothDevice` directly
associated with a `Gatt`, so that `BluetoothDevice` can be treated as a
connectable element.

Via extension functions, the connection state of a "BluetoothDevice" can
be queried, and the state persists across connections (transcends `Gatt`
objects).

Provide `interface` representing non-successful connect (JuulLabs#18)

Allows for simplified connect result checking:

```kotlin
val result = bluetoothDevice.connectGatt(...)
if (result is ConnectGattError) {
    println("Error: ${result.cause}")
}
```

Bump kotlinx.coroutines version to 0.26.1 (JuulLabs#11)

Bumped Kotlin version to `1.2.61`, as the `kotlinx.coroutines`
[GitHub page] states:

> This is a companion version for Kotlin 1.2.61 release.

[GitHub page]: https://github.com/Kotlin/kotlinx.coroutines

Add `timber-logger` project module (JuulLabs#4)

Allows logging of `able` to be configurable via `Logger` interface.
Removes [Timber] dependency from all modules (except `timber-logger`).

[Timber]: https://github.com/JakeWharton/timber

Initial commit