v0.3.0

Changes introduced:

1. combine has been renamed to merge
2. Support for merging annotations only.

Deprecated features:

Post v0.3.0, converter functionality will not be supported. This was motivated by two reasons:

1. There are too many conversion formats. Trying to include even the most popular ones makes the project unwieldy. Better to use one of the readily available scripts online.
2. Until now, the repository only supported TFRecord. Tensorflow is a large library and it does not make sense for it to be a project requirement when it's only used for a singular task of converting to TFRecord.