Kapre

- Add [SpecAugment](https://github.com/keunwoochoi/kapre/pull/135) layer

- bugfix (tflite)

- Add tflite-compatible stft layer

Bugfix for `get_window_fn()`

- `kapre.augmentation` is added
- `kapre.time_frequency.ConcatenateFrequencyMap` is added
- `kapre.composed.get_frequency_aware_conv2d` is added
- In `STFT` and `InverseSTFT`, keyword arg `window_fn` is renamed to `window_name` and it expects string value, not function.
- With this update, models with Kapre layers can be loaded with `h5` file format.
- `kapre.backend.get_window_fn` is added

- `kapre.signal.Frame` and `kapre.signal.Energy` are added
- `kapre.signal.LogmelToMFCC` is added
- `kapre.signal.MuLawEncoder` and `kapre.signal.MuLawDecoder` are added
- `kapre.composed.get_stft_magnitude_layer()` is added
- doc is hosted at https://kapre.readthedocs.io/