Introduce support of add and del operations under erl_opts directive

Add hooks to the upgrade command

Add --start-clean flag to rebar3 shell

Allows override of apps specified in other on-disk options. Equivalent
to `--apps=""`

Fixes #1785

As requested in #1733

Logger OTP-21-rc2 support

Also small output fix in rebar3 shell

Fix override_deps test from suite rebar_compile_SUITE

Auto-boot main app in OTP app project templates

Use maps for child spec example

People are starting to expect these niceties! It's also easier to drop
the config when you know it's there than add it when you don't know it
exists.

Restore default templates in bootstrapped rebar3

When allowing Dialyzer to work internally, we moved a bunch of
config (such as no_debug_info) to the prod profile, but the escript
included files remained locked onto the default profile.

Because the bootstrapping phase now happened in a prod run, the priv/
dirs were never created for the default profile unless a prior run
existed, which hid the bug from us.

This patch overrides the path on the prod profile so that we don't rely
on accidental leftovers for things to work on a bootstrap phase as a
dev.

start at least one async thread in async thread poll

fixes an issue when shell is terminated with an error "Bus error: 10",
on attempt to run rebar shell with verbose logging

Officially drop Erlang R16B support—Logger support in cth_readable, and compact CT output

Required for the Logger interface to be supported since it relies on
maps

cth_readable 1.4.0 supports the new logger interface from OTP-21, which
likely breaks compatibility with R16 builds.

It also includes a new compact interface, displaying output such as:

    ===> Running Common Test suites...
    %%% rebar_alias_SUITE: ......
    %%% rebar_as_SUITE: ...........
    %%% rebar_compile_SUITE:................................
    ............................
    %%% rebar_compile_SUITE ==> test_name: SKIPPED
    %%% rebar_compile_SUITE ==>
    {tc_user_skip,"compile:env_compiler_options/0 available"}
    ..
    %%% rebar_cover_SUITE: .............
    %%% rebar_ct_SUITE: ....................................

Allowing to display more tests within less screen space.
This mode has been added to the ct_readable option under the name
'compact' (now supporting true | false | compact), and has been made
default for rebar3.

Re-disable debug_info on prod profile

Had mistakenly only disabled it for deps.

Work around OTP-21 deprecation of get_stacktrace() and other incompatible changes

see https://github.com/erlang/rebar3/issues/1774

Based off a macro by @okeuday at https://github.com/erlang/otp/pull/1783

ensure dest exists before copying to it and fix src_dirs symlinking

Priv and include dirs need the virtual symlink in order to preserve hook
functionality in some edge cases.

This would cause crashes on linux and force people to have a src_dirs
config that is strictly matching what is on the file system rather than
acting as a specification of those that are valid.

To compare, if lib_dirs worked the same, then any repo that did not both
have apps/ and lib/ would crash, as the spec mentions both options as
valid.

Display warnings when cache dirs are read-only

This should provide more help to users directly and avoid having them go
through opening tickets for help.

Fixes #1767

Clear all dialyzer errors

- this is done by adding a HiPE dependency
- also in this: adding a test for directories, and fixing some indent

Bump cth_readable to 1.3.4: restore eunit macro formatter

Reload apps running in shell with new config