MAINT: Added decorator to tests req. ext. data.
MAINT: Skip data ref tidy-up.
Merge pull request #1044 from cpelley/skip_data

MAINT: Added decorator to tests req. ext. data.
Merge pull request #1045 from pp-mo/agg_eg_fix

Fix in comment in example test.
Merge pull request #1040 from pp-mo/colours_eg

Added a custom colour plotting example.
Fix to link in colorbar example
Merge pull request #1051 from esc24/fixnormlink

Fix to link in colorbar example
Added logarithmic anomaly contouring example.
Incorporate final review improvements to related 'anomaly_log_colouring' example.
Rebased to include pseudocolor gallery example, and cross-refer the two.