Do not apply overrides to a root application.

Overrides should apply to a layer below where they are declared. This
patch makes it so if the project root is an application (i.e. it isn't
'root' and therefore not an umbrella project), we omit applying
overrides in rebar_app_discover.

This in turn required changing a bunch of tests, because all the tests
worked with the idea that all overrides applied to all apps to validate
that they get inherited properly. The changes re-structure the cases so
they are written with an umbrella app, demonstrating that the changes
stick.

OTP-22.0 readiness

- fix some bad typespec
- bump the meck version for good fortune

add support for git ref and file content as app version

supervisor template: add missing comma

remove large comment blocks from templates and use maps in sup

Fix cth_readable crash with bad lager interaction

Disable windows on Cirrus CI

This never passes even if it works on Windows 10 machines and on Circle
CI's runs.

format hex packages in a nice/human way

Signed-off-by: Pierre Fenoll <pierrefenoll@gmail.com>

Signed-off-by: Pierre Fenoll <pierrefenoll@gmail.com>

fixed #2063

Fix duplicate module naming in edoc test suite data

Add basic linting for .app file

add cirrus ci config to test against linux, osx and windows

upgrade relx 3.31.0

Update certifi, ssl_verify_fun, bbmustache

upgrade relx to 3.30.0

support dialyzer plt location and prefix in cli args

rebar3 eunit: Hide slowest tests profile output by default

Enable parallel build

Catch errors in writing the package cache

Fix rebar3 deps command

Deps command shows an * if the local state of the dependencies do not
match the config file, highlighting the differences between the lock
file and the config file if there are any.

Attempt at support sys_config_src in shell

This patch does two things:

1. it broadens the interface for the compiler module so that
   non-first-file modules can possibly be parallelized. This is done by
   dynamically switching on `[ListOfFiles]`, which remains sequential as
   before, or `{[SeqPriority], [Parallel]}`, which divides regular files
   between higher priority ones and those that can be in parallel
2. implements this mechanism in the rebar compiler, based on the erl
   file digraph. If a file has an in-neighbour, it is depended on by
   another file. The mechanism therefore makes it so all files that have
   dependants get compiled in their strict relative sequential order
   first, and then the undepended-on files get compiled together in
   parallel.

By running:

  ./rebar3 ct --suite test/rebar_compile_SUITE.erl --case \
  recompile_when_parse_transform_inline_changes --repeat 50

the previous iteration of this would rapidly fail, and this one succeeds
every time.

Support for parallel compilation of *.erl file was dropped before 3.0 release.
However, our tests for a project containing ~500 source files show substantial gain, lowering compilation time from 58 seconds to 18 on a MacBook Pro 15" (4 cores, 8 threads), and to just 10 seconds on Xeon-D machine.