Update URL to NHANES-database repository

Update metadata README with table changes

Expanded blocklist

Added the human-verified oral health mappings to the blocklist to prevent confusion between human and computer mappings.

Update labels table with onto mapping counts

Update output ontology filepath

Quote values of variables metadata df (closes #24)

Drop the intermediate 'VariableID' column. Output boolean values for OntologyMapped column

Update main.yml

Update ontology table with mapping counts

Add assembled metadata database

Import the tables metadata to the DB

Add metadata sqlite database build

which can be queried using nhanes_metadata_search.py