How to specify an icu tokenizer locale identifier for subclass of sqlite_ext.FTSModel?
It seems that Peewee is quoting the tokenizer (both 2.x and 3.0a), it looks like:

```sql
CREATE VIRTUAL TABLE "note" USING FTS3 ("content", tokenize="icu en_AU")
```

Can you do an experiment for me? Using Peewee (or just the plain old `sqlite3` module):

```python
from playhouse.sqlite_ext import *
db = SqliteExtDatabase(':memory:')
db.execute_sql('CREATE VIRTUAL TABLE thai_text USING fts3 (content, tokenize=icu th_TH);')
```

Or

```python
import sqlite3
conn = sqlite3.connect(':memory:')
conn.execute('CREATE VIRTUAL TABLE thai_text USING fts3 (content, tokenize=icu th_TH);')
```

And let me know what happens? They work well, both of the methods above, by not quoting the tokenizer. Cool I didn't compile sqlite with icu so I wanted to double check that would work. I'll get a patch up today. Thanks! You mind trying out c88fc2ef08c4ed5e7214b7d30f0b20707db43995 and seeing if that resolves the issue? It works! Thanks so much!
Sqlite's built in icu tokenizer supports locale identifier, for example:
```sql
CREATE VIRTUAL TABLE thai_text USING fts3(text, tokenize=icu th_TH)
```
If tried to set `Meta.extension_options = {'tokenize': 'icu th_TH'}`, it will raise error:
```
peewee.OperationalError: unknown tokenizer: icu th_TH
```
Does it support specify this option for subclass of `playhouse.sqlite_ext.FTSModel`?