Develop bug load

This modification corrects a bug that appears when using observations only. Indeed, in that case, it is not possible to use the model mask for the observations since there is no model even if the user requested an interpolation. Therefore the condition nmod >= 1 should be tested whatever the user requests for output=lonlat/lat/lon (then an interpolation is needed) or the user requests explicitely for an interpolation. If nmod == 0, the observed mask would be used ( although a security test to check that this mask has indeed been provided could be good to add)

Develop fix acc doc

The documentation has been updated according to issue #16

Update pdf 2.2.0

Upgrade to 2.2.0

Increased the version number according to SEMVER.
Fixes issue 11.

Merge develop into master

This is an important merge.
After this we all will be able to follow the new developing strategy.
Please @nevensf could you confirm in the discussion below that the features 'Load ice', 'Load obsonly' and 'Plot stereo map' work properly?
Please @cprodhomme could you confirm in the discussion below that the feature 'Plot ACC' works properly?
To confirm that a feature works you can write in a comment 'Feature_name 👍'

Thanks a lot!

Merge removal of unneeded library calls

This is useful so that the package checks successfully in amdahl and moore.
Checked by myself (minor modifications).

Color bar

The addiction of the new parameter cex has been tested by Acacia Pepler and myself. If @vtorralba also agree to test it it would be nice.

Documentation corrections

Some corrections in the sample data documentation

Develop acc

Replacing MR !4
Already tested by Chloé

bugfixe: reverse order of the confidence interval, lower was in position 3 and higher was in position 1