Move entry point to __init__.py

I couldn't find a way to include scripts but pip can automatically
create them from entry-points.

src/procrusql-fit

@@ -1,25 +0,0 @@
-#!/usr/bin/python3
-import logging
-import sys
-
-import psycopg2
-
-import procrusql
-import procrusql.parser
-
-if __name__ == "__main__":
-    logging.basicConfig(format="%(asctime)s %(levelname)s %(name)s %(lineno)d | %(message)s", level=logging.DEBUG)
-    with open(sys.argv[1]) as rf:
-        text = rf.read()
-    ps = procrusql.parser.ParseState(text)
-
-    ps2 = procrusql.parser.parse_ruleset(ps)
-
-    if not ps2:
-        ps.printerror()
-        sys.exit(1)
-
-    db = psycopg2.connect(sys.argv[2])
-    procrusql.fit(db, ps2.ast)
-
-# vim: tw=0

src/procrusql/__init__.py

@@ -1,4 +1,5 @@
 import logging
+import sys
 
 import psycopg2
 from psycopg2 import sql
@@ -241,3 +242,19 @@ def dump_dot():
     for i in range(1, len(in_order)):
         print(f"\t{in_order[i-1]} -> {in_order[i]} [style=dashed]")
     print("}")
+
+def main():
+    logging.basicConfig(format="%(asctime)s %(levelname)s %(name)s %(lineno)d | %(message)s", level=logging.DEBUG)
+    with open(sys.argv[1]) as rf:
+        text = rf.read()
+    ps = procrusql.parser.ParseState(text)
+
+    ps2 = procrusql.parser.parse_ruleset(ps)
+
+    if not ps2:
+        ps.printerror()
+        sys.exit(1)
+
+    db = psycopg2.connect(sys.argv[2])
+    procrusql.fit(db, ps2.ast)
+