CDFTOOLS_3 with CMIP6 capabilities

Release Notes:

• This is really the last tag with CDFTOOLS_3.0.
• Then master branch will be merged with dev_e3t branch to form CDFTOOLS_4.0

This is the last v3 tag, before starting v4

CDFTOOLS tag v3.0.1

• This release has the same user interface as ever. It is published before merging the master with developpment regarding vvl and other improvement/homogeneisation
• use this release for continuity with production scripts using cdftools.

CDFTOOLS before major modifications

CDFTOOLS v3.0.0

This release is the last release which support different mesh_zgr format as input. Further development requires simplication and modification in the treatment of the vertical metrics, in particular for time variation of e3.

A new convertion tool will be available to port old-type mesh_zgr files to the supported one.

Version v3.0.0 can be used with old-type mesh_zgr files.