SQLITE_DATE_TRUNC_MAPPING undefined variable? 
Made a quick fix, the method was out-of-date. This commit fixes the issue: 0416786d56f770c6cec3b9c7493fae7ffd6a75ec Pushed a new version, 3.0.18, which includes the fix. @coleifer thank you for the quick response! No problems, you should have no issues vendoring the peewee.py module, as that's one of the goals for the project -- to make it easy to drop in where you need it.
When using vim I encountered this:

```
F821 undefined name 'SQLITE_DATE_TRUNC_MAPPING'.
```
```
$ git checkout 2.9.2
$ grep -n SQLITE_DATE_TRUNC_MAPPING *
grep: docs: Is a directory
grep: examples: Is a directory
peewee.py:287:SQLITE_DATE_TRUNC_MAPPING = {
peewee.py:294:MYSQL_DATE_TRUNC_MAPPING = SQLITE_DATE_TRUNC_MAPPING.copy()
peewee.py:299:    assert lookup_type in SQLITE_DATE_TRUNC_MAPPING
peewee.py:303:    return dt.strftime(SQLITE_DATE_TRUNC_MAPPING[lookup_type])
peewee.py:4056:        return fn.strftime(SQLITE_DATE_TRUNC_MAPPING[date_part], date_field)
 $ grep -nr SQLITE_DATE_TRUNC_MAPPING *
peewee.py:287:SQLITE_DATE_TRUNC_MAPPING = {
peewee.py:294:MYSQL_DATE_TRUNC_MAPPING = SQLITE_DATE_TRUNC_MAPPING.copy()
peewee.py:299:    assert lookup_type in SQLITE_DATE_TRUNC_MAPPING
peewee.py:303:    return dt.strftime(SQLITE_DATE_TRUNC_MAPPING[lookup_type])
peewee.py:4056:        return fn.strftime(SQLITE_DATE_TRUNC_MAPPING[date_part], date_field)
playhouse/_speedups.pyx:51:cdef dict SQLITE_DATE_TRUNC_MAPPING = {
playhouse/_sqlite_ext.pyx:15:cdef dict SQLITE_DATE_TRUNC_MAPPING = {
playhouse/_sqlite_ext.pyx:29:    if lookup not in SQLITE_DATE_TRUNC_MAPPING:
playhouse/_sqlite_ext.pyx:57:        return result[0].strftime(SQLITE_DATE_TRUNC_MAPPING[result[1]])
```


So in version 2.9.2 it is both in peewee and playhouse ... In version 3.0.17 it is only defined in the playhouse module:
```
$ grep -nr SQLITE_DATE_TRUNC_MAPPING *
peewee.py:2888:        return fn.strftime(SQLITE_DATE_TRUNC_MAPPING[date_part], date_field)
playhouse/_sqlite_ext.pyx:641:cdef dict SQLITE_DATE_TRUNC_MAPPING = {
playhouse/_sqlite_ext.pyx:655:    if lookup not in SQLITE_DATE_TRUNC_MAPPING:
```

If I have some projects which only include `peewee.py` via a local copy, is this going to cause a problem for me ?