don't needlessly update the code path twice if no hooks to run

don't generated coverage for `extra_src_dirs`

closes #1057 and #1179

fix otp-19 bootstrap compiling

upgrade erlware_commons for OTP-19 fix

Fix shell node startup

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