Support for the V ORM

DO NOT MERGE.

This is partial support for the ORM. However, there are some challenges
that need to be addressed before this can be properly reviewed and
landed:

1. The ORM in V requires drivers to be hard-coded. See #90.

2. The Connection doesn't _really_ implement orm.Connection because the
vsql Connection is required to be mut and the current interface
definition does not allow this.

3. We need to create a new test suite for the ORM. `vsql/orm_test.v`
filled with combinations of statements "sql" commands will work just
fine. Specifically, we need to test different combinations of
expressions and types.

Fixes #90

Makefile

@@ -87,6 +87,9 @@ btree-test: oldv
 sql-test: oldv
 	$(V) -stats $(BUILD_OPTIONS) test vsql/sql_test.v
 
+orm-test: oldv
+	$(V) -stats $(BUILD_OPTIONS) test vsql/orm_test.v
+
 # CLI Tests
 
 cli-test: bin/vsql

docs/features.rst

@@ -6,6 +6,7 @@ Features
 
    custom-functions.rst
    in-memory-database.rst
+   orm.rst
    prepared-statements.rst
    server.rst
    transactions.rst