Initial work on use of k-D tree index for ungridded colocation.
Further work in progress for kernel optimisation.
Fix to bug causing output file to be overwritten introduced in 69e84033c0...
Updates to aggregation to get aggregation grid correct for time, and to subset the data before aggregating with Iris so that extra that is outside the grid is not included.
Merge branch 'devel' of proj.badc.rl.ac.uk:jasmin_cis into devel
Merge branch 'devel' of proj.badc.rl.ac.uk:jasmin_cis into devel
Set missing value for Aeronet product (to -999) - Trac #444
Documentation updates, mostly related to aggregation.
Merge remote-tracking branch 'origin/devel' into devel
Merge remote-tracking branch 'origin/devel' into kerneloptimisation

Conflicts:
	jasmin_cis/col_framework.py
	jasmin_cis/col_implementations.py
More work on k-D tree with haversine distances.
Fix to bug causing output file to be overwritten introduced in 69e84033c0...
Updates to aggregation to get aggregation grid correct for time, and to subset the data before aggregating with Iris so that extra that is outside the grid is not included.
Set missing value for Aeronet product (to -999) - Trac #444
Documentation updates, mostly related to aggregation.
Merge branch 'devel' of proj.badc.rl.ac.uk:jasmin_cis into devel
Added aggregation.rst (missing from the previous commit) and updates to plotting documentation
Changed parsing for date/time delta in aggregation to be consistent with that used for colocation and plotting (but behaviour differs - returns an exact tuple rather than converting into days).
Tests for aggregation grid and fixes to the logic for date/time gridding. Updates to the documentation on date and time grids.
Refactored aggregation so that it can be unit tested properly, and is easier to extend to ungridded data. Structure should be more similar to that for subsetting now.