Half-orm

Features

- **Relation:** Add a cast method to cast to another relation type. (d662ccd)
- **halfORM:** The script can now be called without argument inside a half_orm package. (95a4ba0)
- **Model:** Model.relation replaced by get_relation_class now returns a class. (0998253)
- **Relation:** \_\_str__ becomes \_\_repr__. (af6498b)

Bug fixes

- **halfORM:** Fix problem with curly braces in user's code. (7a02309)
- **Fkey:** The FK now references the class in the good scope. (fc304c7)
- **Relation:** Use field.where_repr to have a correct construct of the request with fkeys. (39116a2)
- **Relation:** remove the display of FOREIGN KEY when there is no FK. (89d9c6b)

Features

- **Fkey:** Add tests for foreign keys. (5158ece)
- **Relation:** attributes fields and fkeys are renamed \_fields and \_fkeys. (2e29af0)
- **Relation:** mogrify is renamed to \_mogrify. (3f3541f)

Bug fixes

- **Fkey:** Fix bug in fkey introduced in 3c248a29 by fqrn renaming. (5158ece)
- **Fkey:** Fix is_set pb with fkeys and not constrained relations. (1c6e7d9)
- **Relation:** len wasn't working since Fields introduction. (2e29af0)
- **Relation:** Fix pb with isinstance and Relation objects. (51ff1db)

- First alpha release