Impacted versions:10

Steps to reproduce:
Following the code in https://www.odoo.com/documentation/10.0/api_integration.html both in a fresh install and against 'https://demo.odoo.com/start' trows a type error

Current behavior:
Now I get an error when executing:

```
ids = models.execute_kw(db, uid, password,  'res.partner', 'search',
    [[['is_company', '=', True], ['customer', '=', True]]],
    {'limit': 1})
[record] = models.execute_kw(db, uid, password,
    'res.partner', 'read', [ids])
# count the number of fields fetched by default
len(record)
```

In particular it seems to be a type error (cannot marshal class odoo.tools.float_utils.float_precision)

Expected behavior:
I would expect it to behave as in the documentation

openerp/fields.py
""" Very similar to :class:`~.Char` but used for longer contents, does not
    have a size and usually displayed as a multiline text box.
    :param translate: enable the translation of the field's values; use
        ``translate=True`` to translate field values as a whole; ``translate``
        may also be a callable such that ``translate(callback, value)``
        translates ``value`` by using ``callback(term)`` to retrieve the
        translation of terms.
    """
    type = 'text'
    def convert_to_cache(self, value, record, validate=True):
        if value is None or value is False:
            return False
        return ustr(value)
class Html(_String):