refactor: add sql_keywords filter for custom lowercase_columns macro

 - this macro now safely quotes safewords in use throughout the repo

macros/lowercase_columns.sql

@@ -1,6 +1,14 @@
 {% macro lowercase_columns(column_names) %}
+    {# List of SQL Keywords in use by dbt-synthea #}
+    {% set sql_keywords = ["start", "stop", "type", "system", "date", "first", "last", "value", "name"] %}
     {% for column_name in column_names %} 
-        "{{ column_name }}" AS {{ column_name | lower }} 
+        {% set lowercase_column = column_name | lower %}
+        {# If a keyword - quote the output column name so it can be safely used in models #}
+        {% if column_name | lower in sql_keywords %}
+            "{{ column_name }}" AS "{{ lowercase_column }}"
+        {% else %}
+        "{{ column_name }}" AS {{ lowercase_column }}
+        {% endif %}
         {% if not loop.last %},{% endif %} 
     {% endfor %}
 {% endmacro %}