Half-orm

* Fix 4. Allow args for singleton decorator. (3a3085c)
* fix config file import when HALFORM_CONF_DIR is not absolute (0c54c10)

* Add singleton decorator. (9b643cf)
* README: replace . (d075977)

* [doc] Add return value on insert. (6a70c56)
* Add warning when trying to call a Field. (86243da)
* [CI] .gitlab-ci.yml. test stage. (364b823)
* Replace format with f strings. (c45463b)

0.5.9. (2021-12-01)
* Quote columns names in SQL update. (7056b98)

0.5.8. (2021-10-12)
* [model] Add attribute production. (6046432)

* [relation] join: only format to string instances of classes listed in TO_PROCESS. (cc81112)
* [relation] join method now raises an exception if the relations are not connected. (9152506)

0.5.6. (2021-09-22)
* [relation] join method. (4dd6286)

* Add Model.diconnect method. (70af38e)

* Add support for partitioned tables. (9106143)
* [relation] _mogrify now triggers the print of the SQL query when a DML method is invoked. (0e66601)
* Add Relation.is_empty method (faster than len(relation) == 0). (08ec57a)