that allows to initialize the database for a given swh package with db
connection credentials/dsn read from a standard swh config file.

Also add a couple of tests (only tests click group and command exist).

Closes T1896.

and document it briefly in the README file.

This comes with a few checkers:
- flake8
- trailing-whitespace
- check-json
- check-yaml
- codespell

Also include commented checkers:
- black: disabled since we are not ready for this yet,
- pydocstyle: disabled since we have way too many pydoctyle errors for now...

See https://pre-commit.com/ for more details.

Related to T1881.

No need for it being a dynamically defined function, plus it makes pydocstyle
very unhappy (probably a bug in pydoctyle 4.0.0 but...).

Also rename it as _safemembers() for consistency sake.

use a newly created event loop to consume events in test_timed_coroutine.
ome reason, executing this later test in the same test session as
swh/core/api/tests/test_async.py fail because the main event loop seems
to be closed by the test.

json.loads() expect a str, not a bytes.

Note that test_post_struct_json is failing with current implementation,
the fix comes with the next revision.

- SWHRemoteAPI -> RPCClient
- SWHServerAPIApp -> RPCServerApp

to get rid of the SWH prefix and give them more consistent names, especially
the swh.api.asynchonous.SWHRemoteAPI class which is very confusing.

Deprecate old class names using the Deprecate python module.

by default:
- increase the connection pool size and
- set retry to 3 (number of retries each connection should attempt).

These config params can be set directly from config files for 'remote'
api clients. For example, to specify these in an objstorage client
config file:

  objstorage:
    cls: remote
    args:
      url: swh-objstorage:5003
      max_retries: 5
      pool_connections: 100

this is needed to prevent the command to depend on having pg's createdb
tool installed on the machine running the 'swh db-init' command.

In a normal deployment setup, this pg tool is not expected to be present
on every machine on which one want to be able to use this 'swh db-init'
command.

we want the root logger configured there, not the cli one.

to make sure each extra setup dependencies are ok.
This requires to move test files in its related subpackage.

Warning: this may break swh packages that depends on swh.core which have
not been updated to swh.core 0.0.60.

Note that for now, the main requirements.txt still contains all the
dependencies for backward compatibility reasons.
This will have to be fixed once all packages that depends on swh.core
have been updated.

closes T1678.

This allows to declare click-based subcommands using the setuptools'
entry point "swh.cli.subcommands".

The main "swh" command group does only handle the "--log-level" option.

Also extract the db-init command in a dedicated submodule and ensure both
  swh db-init
and
  swh-db-init
work.

Related to T1671.

so that 3rd-party ones are in a dedicated 'section' as described in PEP8

  https://www.python.org/dev/peps/pep-0008/#id23

So they gracefully release the connection on error instead
of relying on reference-counting to call the Db's `__del__`
(which does not happen in Hypothesis tests) because a ref
to it is kept via the traceback object.

using an incremented counter, instead of pushing an inacurrate timing
data (if calling the encapsulated function raises an exception).

pushing streamed content should not imply the result is streamed.

- add a default implementation of the exception class
- make the exception class a class attribute of SWHRemoteAPI that can be
  overloaded at instanciation time by the api_exception named argument
- so the api_exception positional argument of SWHRemoteAPI becomes a named
  argument

WARNING: This later point does break compatibility for any use of this class
not using named arguments when instanciating it. Fortunately, as far as I
know, every swh packages does use named argument when instanciating this
class, so this should not break anything.

- ensure we do accept **kwargs so any super().__init__(**kwargs) from an
  unexpected MRO path in an indecent maze of multi-inheritance will not crash
- do not call super().__init__(); it is either useless (most probably,
  super() is object in this context) or silently ignore passed kwargs that
  super() (when it's not object) may have been able to understand...

Long story short, kwargs handling in multi-inheritance __init__ methods is
a mess.

- merge raw_post and row_get in a unique raw_verb method,
- merge post_stream() and post() as a unique post(); post_strean is then a
  call to post with the 'stream' parameter set,
- merge get_stream() and get() the same.

so the pytest-postgresql fixture works as expected on non C locale systems.

we almost never return text/plain or text/html, so json is a better default
value.

for debugging purpose.