Feature request: provide feedback if Model.save() succeeded
Peewee doesn't try to be too clever here, but you're right, the update statement will fail silently, which I agree is bad.
 Fixed in e73d3db12fb370c48cca8f45514a7fed9637949c -- returns number of rows affected (1 always in case of inserts, but could be 0/1 for updates).
 Cool, thanks a lot.

The current implementation of [Model.save()](https://github.com/coleifer/peewee/blob/master/peewee.py#L3071) does not provide any feedback if the save operation failed or succeeded. In the case a retrieved record has been deleted by a concurrent process in the meantime, the executed UPDATE statement finds no matching record and "fails" silently.

**Proposal 1**
The Model.save() implementation should be changed so it returns the number of affected rows by the executed SQL statement. This allows developers to ensure a successful save operation.

**Proposal 2**
The Model.save() implementation should be changed so it raises an exception in the case the number of rows affected by the UPDATE statement is not 1.

Example describing the issue:

```
from peewee import *

db = SqliteDatabase('example.sqlite')


class BaseModel(Model):

    class Meta:
        database = db


class Foo(BaseModel):
    bar = CharField()


def init():
    db.connect()

    Foo.create_table(True)


def close():
    db.close()

init()

# Prepare sample for test
f = Foo.create(bar='Lorem ipsum')
f.save()

f1 = Foo.get(Foo.bar == 'Lorem ipsum')
f2 = Foo.get(Foo.bar == 'Lorem ipsum')

f1.delete_instance()
f2.bar = 'dolor sit'

# Saving a record deleted in the meantime does "fail" silently
f2.save()

close()
```
