Handle force flags in leading position

The checking of flags and the parsing of arguments is separated up.

Ct output improvements

- eunit assert look better
- lager logs to the html logs

upgrade eunit_formatters to 0.3.1 for OTP18 bug fix

only add package list of versions to registry if it has the right build tool support

upgrade eunit_formatters for OTP 18 support

warn on incorrectly specified test options in `rebar.config`

when `ct_opts`, `eunit_tests`, `eunit_first_files`, `ct_first_files`, `erl_first_files`,
`eunit_compile_opts`, `ct_compile_opts` and `erl_opts` have values that are single non-list
terms warn and try wrapping them in a list when processing them in the `eunit` and `ct`
providers

Fix error reports on missing include paths

In some cases (nested includes?) paths end up in such a way that joining
them breaks up and hard-crashes rebar3. This patch specifically handles
this scenario to fix things by avoiding passing empty lists to
filename:join.

Update cf

Fix IO locking up in shell apps

Application masters are booted at the root of apps, and take over the
group leader role to redirect IO. To cut the chain short and properly
have their role inherited, they are their own leader, and keep a
reference to the old leader in their internal state, which we cannot
change.

This is done so process ownership to a given application can be
established, and allows to properly clean up resources outside the
supervision tree when an app is shut down.

This patch goes around and finds all processes whose group leaders are
application masters older than the new `user' process booted by the
shell providers, and swaps them with that new `user'. This lets the
application masters survive, and fixes the blocking IO issue
(resolving issue #899)

This may mean an incomplete clean up is down on application shutdown,
but that seems like a fair compromise.

include Sean Cribbs eunit formatter by default

rebar3 shell improvements (escript, rebar.config shell defaults)

Adds the ability to run an escript before starting the apps and
interactive shell for a project. This is intended to improve the
local development experience for projects by providing an easy way to
run companion services (mock rest APIs, databases etc) that the
project relies on.

This patch also adds {shell, Defaults} to the rebar config file so
that a project can supply default values for many of the new or
improved 'rebar3 shell' options:
* {apps, OTPApps}
* {script_file, EscriptFileName}
* {config, ConfigFileName}

The order of option precedence is command line, rebar.config, relx.

Prettify all of common test output.

This uses cth_readable to:
- silence error_logger output to the shell unless a test fails
- silence ct:pal output to the shell unless a test fails

I have currently not baked in any way to disable this behaviour, but I
figured if it is required, there is time to do it before the final
3.0.0 release.

fix typo of guarantee. h/t evan

do not sort mib_first_files during merge_opts, order must be kept

upgrade relx to 3.8.0, fixes bug in upgrade_install escript

calculate coverage info as late as possible in ct provider execution

fixes for cover under new compiler/eunit/ct

rebar_prv_common_test refactor

* remove partial support for ct `test_spec` until it can be done properly
  and warn if `test_spec` is present in test opts
* use new compiler functionality to reduce complexity of provider
* reduce command line options available to those that can be
  supported properly

fix #903: use app discover of entire plugins dir when listing

Rebuild PLT when beams no longer exist

add an option to soft purge rather than purge old code