Resolve TODOs and formatting of Handler module

Resolve the TODO comments regarding logging output in the Handler
module and, at the same time, the code formatting, comments and
organisation.
Comments and log delete init doc number
Use prisms to clean up and reduce code related to Retcon.Diff
Merge remote-tracking branch 'origin/master' into wip-cleanse-handler

Conflicts:
	lib/Retcon/Handler.hs
Merge pull request #70 from anchor/wip-use-prisms-on-diffs

Use prisms to clean up and reduce code related to Retcon.Diff
Merge pull request #65 from anchor/wip-cleanse-handler

Resolve TODOs and formatting of Handler module
Split "args" from "options" in command-line

Separate the data types and parsers for the configuration-y "options"
and the command-y "arguments".

This results in parsers which are more readily reused in client code.
Move all DataSource related of of the things to core
Merge pull request #72 from anchor/wip-move-data-source-to-core

Move all DataSource related of of the things to core
Merge pull request #71 from anchor/wip-split-config-parsers

Split "args" from "options" in command-line
Merge remote-tracking branch 'origin/master' into wip-dont-ignore-entity

Conflicts:
	lib/Retcon/Handler.hs