Changed play() and prepareRecordingAtPath() to use absolute paths to audio files

[wootwoot1234]

Changed play() and prepareRecordingAtPath() to use absolute paths to audio files.

Added AudioUtils module for creating paths to files. AudioUtils has constants: MainBundlePath, CachesDirectoryPath, DocumentDirectoryPath, LibraryDirectoryPath. Since the constants are used in both play and record it seemed cleaner to create AudioUtils.

Fixed typo with encoding code, had "caf" as default AudioEncoding type but should be "ima4", "ima4" is the audio encoding for "caf" files.

Here's an example of how to use the new constants.

    var {AudioRecorder, AudioPlayer, AudioUtils} = require('react-native-audio');

    // for recording
    var options = {
        SampleRate: 16000.0,
        Channels: 1,
        AudioQuality: 'Medium',
        AudioEncoding: 'aac',
    };
    var audioPath = AudioUtils.DocumentDirectoryPath + '/filename.m4a';
    AudioRecorder.prepareRecordingAtPath(audioPath, options);

    // for playing
    var audioPath = AudioUtils.DocumentDirectoryPath + '/filename.m4a';
    AudioPlayer.play(audioPath);

[jsierles]

AudioUtils is perfect - I wanted to do that anyway. It would be even better if this were a common library that other plugins could use. I thought about using react-native-fs but it may be too heavy a dependency.

Anyway I'll add docs about the breaking change, and we can bump to 1.0.0. If you can, could you look at updating the AudioExample project? If not I'll take a look.