ODB functions

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

`append()`	Appends the given data to file
`file()`	Returns a file handler for the specified filename
`odb_filter()`	Filters `Odb` data
`odb_visualiser()`	Defines visualisation for `Odb` data
`read()`	Reads the given file and returns a variable of the appropriate type
`retrieve()`	Retrieves data from MARS
`write()`	Writes/appends the given data to file