ODB functions

This is the list of all the functions related to Odb data.

`append()`	Append the given data to file
`file()`	Return a file handler for the specified filename
`odb_filter()`	Filter `Odb` data
`odb_visualiser()`	Define visualisation for `Odb` data
`read()`	Read the given file and returns a variable of the appropriate type
`retrieve()`	Retrieve data from MARS
`write()`	Writes/appends the given data to file