`rebar3 path' provider

support updating of per app info by hooks

upgrade providers, new version gives error message for bad provider dep

hooks/artifacts are always run/resolved from an app unless at top of umbrella

Fix cover_spec options for ct

delete and prepend code path instead of replacing, fixes #770

add current_app attribute for setting before calling hooks

Fix #744: Allow _checkouts dep to override pkg dep not in registry

move state into app_info

Revert "Revert "only load packages when needed""

Revert "only load packages when needed"

only load packages when needed

Displays package caching actions

use ~ts for unicode output and reset encoding to latin1

as default seperator

Utf8 tree

This makes it obvious where packages are cached and when the cache is
being reused.

Messages are of the form:

===> Fetching recon ({pkg,<<"recon">>,<<"2.2.0">>})
===> Downloaded package, caching as
$HOME/.cache/rebar3/hex/default/packages/recon-2.2.0.tar

and

===> Fetching recon ({pkg,<<"recon">>,<<"2.2.0">>})
===> Version cached at
$HOME/.cache/rebar3/hex/default/packages/recon-2.2.0.tar is up
to date, reusing it

prints requested paths to stdout based on current profile

set parent on already fetched apps so tree works

Use raw bytestream when writing files