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Update the release notes (readme.rst) for the ARM Trusted Firmware v1.4 release.

Also, reorder and fix some of the links following the conversion to
reStructured text format.

Change-Id: I8f5e8aa86cb891f61b6b62cf9fab0ad0f0ebb36b
Signed-off-by: Dan Handley <dan.handley@arm.com>