lib/sqlite3: rename low-level module to native_sqlite3.nit

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/sqlite3: rename classes of sqlite3_native to prevent conflict with Nity versions

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/sqlite3: column_text returns a NativeString at low-level

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: rename and update low-level sqlite3 test

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/sqlite3: intro nity interface

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/sqlite3: add some shortcut methods

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: add a test for the Nity sqlite3 module

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>