Merge - HiRid - Take only top 300 hundred medications

[PavanReddy28]

Implementation

Added support for AUTOMATIC_MAPPING_HIRID to take only the top 300 medication in HiRiD dataset like for MIMIC III, as part of the below commits.

• https://github.com/dancoster/DrugLab/commit/cba1f42c8c0cd22269198f6e7d38c8bb3b35ccb7
• https://github.com/dancoster/DrugLab/commit/7a3a916d456509480d77b88a9069569f51fa9809