Refactor project structure

This follows guidance from several well-known Python best practices
guides. Basically, the idea is create a package for the application
that is comprised of several re-usable modules.

See: https://docs.python-guide.org/writing/structure/
See: https://realpython.com/python-application-layouts/

README.md

@@ -24,11 +24,11 @@ Set up the environment variables for Solr and PostgreSQL:
 
 Index the Solr statistics core to populate the PostgreSQL database:
 
-    $ ./indexer.py
+    $ python -m dspace_statistics_api.indexer
 
 Run the REST API:
 
-    $ gunicorn app:api
+    $ gunicorn dspace_statistics_api.app:api
 
 Test to see if there are any statistics:
 

dspace_statistics_api/app.py

@@ -1,4 +1,4 @@
-from database import database_connection
+from .database import database_connection
 import falcon
 
 db = database_connection()

dspace_statistics_api/database.py

@@ -1,7 +1,7 @@
-from config import DATABASE_NAME
-from config import DATABASE_USER
-from config import DATABASE_PASS
-from config import DATABASE_HOST
+from .config import DATABASE_NAME
+from .config import DATABASE_USER
+from .config import DATABASE_PASS
+from .config import DATABASE_HOST
 import psycopg2, psycopg2.extras
 
 def database_connection():

dspace_statistics_api/indexer.py

@@ -30,10 +30,10 @@
 # See: https://solrclient.readthedocs.io/en/latest/SolrClient.html
 # See: https://wiki.duraspace.org/display/DSPACE/Solr
 
-from database import database_connection
+from .database import database_connection
 import json
 import psycopg2.extras
-from solr import solr_connection
+from .solr import solr_connection
 
 def index_views():
     # get total number of distinct facets for items with a minimum of 1 view,

dspace_statistics_api/solr.py

@@ -1,4 +1,4 @@
-from config import SOLR_SERVER
+from .config import SOLR_SERVER
 from SolrClient import SolrClient
 
 def solr_connection():