day of year constraint
review actions
String serialization of collapsed coordinate.
ENH: Fields file loader grid type extended interp.

The fields file loader now handles grid type 29 and 27 correctly and
also interprets specifically the horizontal grid type variable when set
to global.
MAINT: Review actions made.
Merge pull request #849 from cpelley/vector_coord_lbc

ENH: Fields file loader grid type interpretation extended.
ENH: Scalar coord promotion util.
Merge pull request #848 from cpelley/scalar_time_netcdf

ENH: Scalar coord promotion.
Merge pull request #847 from bjlittle/collapse

String serialization of collapsed coordinate.
Fallback to REAL constants where necessary.

For FieldsFile fields with no BDX, BDY and no X, Y vectors,
use the values in the file's REAL_CONSTANTS section instead.
Merge pull request #839 from bblay/dayofyear

Added experimental a "day of year" constraint.
Add abstract definitions
Comment and test name tweaks
Push regular_x/y methods to superclass
Revert handling of horiz_grid_type
name to grib
review actions
Fix typo and tweak test name
Use ubuntugis stable.
Merge pull request #857 from bjlittle/travis_gdal_fix

Switch to ubuntugis stable.