feat: paper downloading pipeline

[shloknatarajan]

Download XML PubMed Article from PMCIDs

Updates

1. Downloads data at PharmGKB's variantAnnotations API ("https://api.pharmgkb.org/v1/download/file/data/variantAnnotations.zip")
2. Get's all the unique PMIDs from the annotated data
3. Converts them into PMCIDs (based on what's listed as available from NCBI's ID Converter API
4. Downloads the available articles into the src/fetch_articles/saved_data/articles
5. Updated to src structure and created many readme changes

Next Steps:

1. Upload saved articles somewhere
2. Create a benchmark for extracting annotations from files. This will involve coming up with metrics and creating an evaluation pipeline

[gtcha2]

merging request, but will need to fulfill the reuse and the pylint before going public,