New pp rule to calculate forecast period.
Added ESMPy conservative regrid.
Merge pull request #453 from pp-mo/esmf_conserve

Conservative regridding using ESMPy
BF - handle missing values from grib messages
Merge pull request #520 from ajdawson/grib-missing-values

BF - handle missing values from grib messages
Moved to SHA for iris-test-data until we tag the next release.
Merge pull request #523 from esc24/travis_test_data_bump

Moved to SHA for iris-test-data until we tag the next release.
Modified plot.py to pass coords arg through to _map_common()
Review actions.
Revised grib load+save: extra levels translation, and grib <-> cf phenomenon translation from metadata project.
Merge pull request #482 from pp-mo/grib_translation

Revised grib load+save
Review actions.
Merge pull request #463 from esc24/plot_coords_keyword_fix

Plotting still uses map where possible even when 2D lat/lon are present.
Allows `coords` argument to select map coordinates when multiple options exist.
Fixes #448 and #468.
Review actions
Merge pull request #514 from esc24/pp_save_missing_fp

New pp rule to calculate forecast period.
Adds support for ieee 32bit fieldsfiles to iris.load
Added a ieee32 fieldsfile test.
BF - preserve masked arrays during aggregation
Merge pull request #527 from ajdawson/aggregate-missing

BF - preserve masked arrays during aggregation
Merge pull request #297 from pelson/ieee_32bit_fieldfile_support

Adds support for ieee 32bit fieldsfiles to iris.load