Fourth, and hopefully last Beta

Backwards incompatible changes in beta-4 (since beta-3):

• changed support for a few features and options in ct and eunit
• eunit and ct have a new fancier output format; can be disabled on demand.
• shell_apps option is now the shell option within the app tuple.

Changelog:

• rebar3/852: print a warning if a profile in 'as' has no config entry
• rebar3/854: if not in a git repo but have 'git' as vsn, fallback to 0.0.0
• rebar3/856: add ERLANG_ARCH and ERLANG_TARGET to os env for hooks
• rebar3/858: don't include certifi priv dir in escript, it is not needed
• rebar3/864: Support proper paths in non-erl first files
• rebar3/867: Fix for issue #859 - unicode rendering of deps tree based on PR #865
• rebar3/877: Allow non-default checkouts dir for relx
• rebar3/881: Bump cf for fixing #879
• rebar3/883: compiler refactor/eunit & ct fixes
• rebar3/886: return more useful error message (failed to download) when pkg http req fails
• rebar3/890: only clean project apps once even when doing --all
• rebar3/893: rebar3 shell improvements (escript, rebar.config shell defaults)
• rebar3/894: rebar_prv_common_test refactor
• rebar3/895: delay validation of eunit tests until just before running
• rebar3/896: move test profile bootstrap into core
• rebar3/898: dedup src_dirs and extra_src_dirs on read
• rebar3/900: Rebuild PLT when beams no longer exist
• rebar3/901: prevent rebar3 from reloading it's own path and terminating itself
• rebar3/904: add an option to soft purge rather than purge old code
• rebar3/905: fixes for cover under new compiler/eunit/ct
• rebar3/906: fix #903: use app discover of entire plugins dir when listing
• rebar3/907: calculate coverage info as late as possible in ct provider execution
• rebar3/911: upgrade relx to 3.8.0, fixes bug in upgrade_install escript
• rebar3/912: do not sort mib_first_files during merge_opts, order must be kept
• rebar3/915: fix typo of guarantee. h/t evan
• rebar3/917: Prettify all of common test output.
• rebar3/918: include Sean Cribbs eunit formatter by default
• rebar3/919: Fix IO locking up in shell apps
• rebar3/920: Update cf