Implement model serialization & loading. Enable in learning command.

[malcolmgreaves]

Do:

1. Implement a model serialization format for the SVM used in relation learning.
2. Use this format and enable the learning command to output the model.
3. Use this format and enable the extraction command to accept a previously trained model.

The relation extraction model serialization format will need to have:

• The candidate generation method used (or a reference to the method).
• The entire feature set, with indices, used in the SVM.
• The learned weights for each feature.