- add function that allows the complete removal of an entry from auth
 config

 - add test for rebar_hex_repos:remove_from_auth_config/2

 - update test/rebar_pkg_repos_SUITE:auth_read_write_read/1 to use mocks so
 we don't append to actual hex.config files

fixes tsloughter/rebar3_hex#184

- Vendor in hex_core at v0.6.8
 - Rename checksum to inner_checksum and deprecate in favor of new outer_checksum key/val
 - Change warn_vsn_once/0 to warn_vsn_once/1 so we can give a proper error message and
   take appropriate action.
 - Update rebar.lock to 1.2.0 format with continued support third-party
   that still may make use of inner checksum via continued persistence of
   inner checksums.
 - Changed app info tuple (package representation) to support inner and
   outer hashes for backwards compat support (see above)

- vendor in hex_core at v0.5.0
  - Change where repo_name should be the org and not the parent
  - Changed rebar_utils:url_append_path/2 to not explicitly add a '?',
    this is returned in the Query chunk by http_uri:parse/1 (e.g., "?foo=bar")
  - update organization_merging test to expect the sub-repo as the repo_name
  - Add tests for rebar_utils:url_append_path/2
  - Stop referencing/setting "organization" in config and use new
     organization settings (api_repository and repo_organization)
  - Do not set (assume) the read key is valid for any/every repo
  - Set repo_organization and api_repository to org
  - Update tests to check for new config opts

- Modified rebar_hex_repos:auth_config/1 to abort on error except in
 the case of enoent, in which we return an empty map.
 - added auth_config_errors test to test/rebar_pkg_repos_SUITE

retired packages are now used the same as any other but
a warning will be printed when it is resolved.

prerelease versions are skipped unless explicitly given
as the version in the constraint or lock file.

* update to hex_core for hex-v2 repo support (#1865)

* update to hex_core for hex-v2 repo support

This patch adds only single repo hex-v2 support through hex_core.
Packages no longer filtered out by buildtool metadata and the
package index is updated per-package instead of fetched as one
large ets dump.

* tell travis to also build hex_core branch

* support list of repos for hex packages (#1866)

* support list of repos for hex packages

repos are defined under the hex key in rebar configs. They can be
defined at the top level of a project or globally, but not in
profiles and the repos configured in dependencies are also ignored.

Searching for packages involves first checking for a match in the
local repo index cache, in the order repos are defined. If not found
each repo is checked through the hex api for any known versions of
the package and the first repo with a version that fits the constraint
is used.

* add {repos, replace, []} for overriding the global & default repos

* add hex auth handling for repos (#1874)

auth token are kept in a hex.config file that is modified by the
rebar3 hex plugin.

Repo names that have a : separating a parent and child are considered
organizations. The parent repo's auth will be included with the child.
So an organization named hexpm:rebar3_test will include any hexpm
auth tokens found in the rebar3_test organization's configuration.

* move packages to top level of of hexpm cache dir (#1876)

* move packages to top level of of hexpm cache dir

* append organization name to parent's repo_url when parsing repos

* only eval config scripts and apply overrides once per app (#1879)

* only eval config scripts and apply overrides once per app

* move new resource behaviour to rebar_resource_v2 and keep v1

* cleanup use of rebar_resource module and unused functions

* cleanup error messages and unused code

* when discovering apps support mix packages as unbuilt apps (#1882)

* use hex_core tarball unpacking support in pkg resource (#1883)

* use hex_core tarball unpacking support in pkg resource

* ignore etag if package doesn't exist and delete if checksum fails

* add back tests for bad package checksums

* improve bad registry checksum error message