Añadimos tabla iva y retencion

"""
Tabla iva
"""
dbRosan.define_table("iva",
      SQLField("descripcion", "string", length=100, notnull=False,
default=None),
      SQLField("valor", "double", notnull=True, default=None),
      SQLField("activo", "boolean", notnull=True, default=True))

"""
Tabla retencion
"""
dbRosan.define_table("retencion",
      SQLField("descripcion", "string", length=100, notnull=False,
default=None),
      SQLField("valor", "double", notnull=True, default=None),
      SQLField("activo", "boolean", notnull=True, default=True))