Coroutine support

New : Arrow shape
Change : (Breaking Change) minSdkVersion changed to 21
Change : (Breaking Change) Shape names are no longer UPPERCASE
New : Suspending functions for saving images: saveAsFile(String[, SaveSettings]) and saveAsBitmap([SaveSettings])

// Please note that if you call this from a fragment, you should call
// 'viewLifecycleOwner.lifecycleScope.launch' instead.
lifecycleScope.launch {
    val result = photoEditor.saveAsFile(filePath)
    if (result is SaveFileResult.Success) {
        showSnackbar("Image saved!")
    } else {
        showSnackbar("Couldn't save image")
    }
}

Fixed : #374 IndexOutOfBoundsException when saving bitmap