Added the datatype date, time and datetime
Moved all custom erros to a single file
Cleaned code to be more readable and created some small utils
Other stuffs that I dont recall. Basically preparing for the
relationship implementation
Started by doing a SchemaEngine but at the end I just put everything
inside the FileEngine.
Now you can use 'schema init path/to/schema' to initialize the struct
folders and first data file, Also save a copy of the schema in a file in
the ZipponDB folder.
