This will allow us to eventually change the default type without it
looking ridiculous.

By default rebar3 displays compiler sources as absolute paths in their
original location, which is under the build dir.

This change introduces an option 'compiler_source_format' to format
sources in two alternative ways:

    relative
    absolute

When either 'relative' or 'absolute' are specified, the file is
resolved to its original location when it is a link. When 'relative'
is specified, the path is displayed relative to the current working
directory. When 'absolute' is specified, the path is absolute.

The default value is 'unchaged' which leaves the compiler source
unchanged.

This is arguably too flexible as I suspect most people would opt for
'relative' all the time - it's the most compact representation of the
file and is sufficient to find the source given cwd. The change
however is meant to introduce the change gradually, preserving
existing behavior and giving users a choice for formats.

In time perhaps the default can be changed to 'relative' - but still
allowing users to revert to the other two options ('absolutel' and
'unchanged') as needed.

Add support for xref_ignores

Allows overwrite default cache dir using REBAR_CACHE_DIR

Fixes logging from remote shells in rebar3 shell

Add a provider hook for edoc

Change to new hex.pm repo URL

upgrade relx to 3.19.0

Allows `pre_hooks` and `post_hooks` to fire for the `edoc` provider.

Somehow swapping the tty handler once more fixes everything. I guess we
were missing a step somehow.

upgrade relx and erlware_commons

supported dist_node in ct and eunit

Recursively load configurations in shell

The sys.config loading in the shell command did not implement recursion
and thus processed the file different from a `erl -config cfg/path`.

Instead of reading every time that rebar_dir:global_cache_dir/1 is
called

Blacklist apps to reload

When an app contains one of the modules we can't afford to get upgraded
without breakage (i.e. erlware_commons, providers, getopt), skip
reloading that application from the rebar3 agent, such that it can keep
on working in subsequent calls.

Blacklisted:

- erlware_commons (broke on ec_cmd_log)
- providers (core to functionality)
- cf (useful to not explode on colors)
- cth_readable (only used for CT suites, but incompatibilities may break
  whole runs)

Fixed git version bug

I've tried to compile project with git in .app.src vsn
Project was tagged as 1.0.0, but resulting .app vsn becomes 1.0.0+build.6.reff0aec24

```git lg
* f0aec24 - (80 минут назад) Fixed ct — Kozlov Yakov (HEAD -> master, tag: 1.0.0, origin/master)
... 5 commits before
```

```
$ git log --oneline --no-walk --tags --decorate
f0aec24 (HEAD -> master, tag: 1.0.0, origin/master) Fixed ct
```

I've found that `HEAD -> master` doest match pattern in [rebar_git_resource](https://github.com/erlang/rebar3/blob/master/src/rebar_git_resource.erl#L204)

allow all `ct_opts` arguments to be passed through to `ct:run_test/1`

Extract dist config handling, support {dist_node, ...}

change travis config to only upload escripts for tags (stable releases)

Cosmetic change: remove last comma-first style

This commit moves the handling of distribution config and starting out
of rebar_prv_shell and into rebar_dist_utils. The module is able to
handle standard config options and boot a distributed node mode. This
could be used in plugins (once it is exposed) and other providers like
CT.

Configuration is also expanded so that options like:

    {dist, [{sname, atom()}, {name, atom()}, {setcookie, term()}]}

can be used and will be handled as a default. The config handler
supports similar terms from the command line being parsed in if the
calling provider supports them.

A test suite is added for configuration handling.

rebranding: update links rebar/rebar3 -> erlang/rebar3

Fix Travis build status image in readme

Support all deps & locks in rebar3 path

Allow 'rebar3 pkgs <app>' to return only that app

Fix bugs/race conditions in shell

Unsure if this should be a final supported format or if we should
support other ways to match instead.

This is a demo to solve the issue hilighted in
https://github.com/erlang/rebar3/pull/1072

By default, the dependency only handled versioned packages and top-level
source dependencies, and locks were being ignored.

This patch makes it so locks and package deps are being considered,
generating full-blown path lists.

Should fix #1117

Following suggestions from @psyeugenic, this code terminates and waits
for the termination of the port handling IO before booting our own,
which should get rid of annoying warnings.

We also allow for the failure to shutdown the user worker under
kernel_sup, since it is likely not there anymore in many scenarios,
preventing crashes.

Allows overwrite the default cache directory using the environment
variable REBAR_CACHE_DIR.