MAINT: No further updates to changelog.

Currently the iris whatsnew purpose overlaps with the changelog and
thus the changelog has no clear purpose.  For developers it has been
agreed that for them to analyse the commit history would serve the
intended use of a changelog.
Merge pull request #760 from cpelley/rm_changes

MAINT: Remove iris changelog.
Created v1.5.0
Merge pull request #761 from pelson/v1.5.x

Created v1.5.0
Added support for comparison with numpy types.
Merge pull request #781 from esc24/extract_fix

Extract fix
Corrected code path for extract(model_level_number=cell)
Merge pull request #782 from esc24/extract_fix_tuple_comp

Extract fix for Cell comparison
Changes for v1.5.1
Updated version to v1.5.1
Version updated to v1.5.2-dev
Merge pull request #789 from dkillick/Version_1.5.1

Version 1.5.1
merge 1.5.x
Merge pull request #809 from bblay/merge_151

Merge 1.5.x branch