for writeas-cli and wf-cli.

add accounts command

Resolves T672

This replicates behavior elsewhere, where we don't output anything if
there is no information to show. Instead, the "no accounts" message will
only show if the user supplies a -v / --verbose flag.

- Remove description
- Fix usage (it only shows drafts)
- Remove --md flag (Markdown is always rendered on draft posts)
- Fix --verbose description

this adds a new sub command accounts, which will list all currently
authenticated user accounts grouped by hostname

This isn't needed / used in WriteFreely.

Support any writefreely instance

Resolves T586 T594 T595 T635

this adds a new sub command accounts, which will list all currently
authenticated user accounts grouped by hostname

this changes DoUpdate and DoDelete to load the user and set the access
token in the client when no edit token is provided.

this adds a check for any logged in users on any host when neither the
user or host flag are passed and not default pair is configured

if the user flag is provided auth should attempt to authenticate with
that user.

previously when the user flag was provided, the function would still try
to get a user from config. flag should take precedence

this adds a check for configured defaults during the command pre check
when authentication is required. using the values found if both are
present and only if both flags are ommitted.

now that the scheme is not required in the configuration file, we can
assume the configured value is correct. as with other uses, the
configured value is only used when noth host and user are present.

if both a user and host are configured, the command auth should assume
that user and host when none specified

this updates newClient to prepend the scheme https to the default host
found in the global config, and only use said host when both the user
and host are configured

by needed: when host flag was supplied, matches that configured and a
user is set in config as well. they should be a pair.

this uses the usersLoggedIn helper to check for already logged in users,
selecting the single user when only one present and returning and error
when multiple are logged in.

this function checks the host based path for any logged in users and
returns the number or users, a list of usernames and an error if any

for use outside of package

to start on a fix for user actions when logged in with one user on a
given host with the wf binary, a user should now only be loaded by the
caller of newClient.

newClient no longer takes a bool for authRequired, all calls
updated to new signature and load the user where required.

On logout, this deletes host / user directories if they're empty.

Ref T586

WriteFreely doesn't support non-auth'd posting like Write.as, so users
won't be creating non-auth'd posts with another client that they'd need
to add here.

Ref T586

Now when running `wf auth`, we'll automatically set the given host +
username as the default account in .writefreely/config.ini, so subsequent
requests without an explicit --host and --user will use this account.

Ref T635 T586

Previously, this would always include writeas-cli.

Ref T586

Unlike Write.as, WriteFreely doesn't support anonymous (unauthenticated)
publishing. With these changes, we reflect that in wf-cli by wrapping
creating, updating, and deleting posts in a func that checks
authentication state.

Ref T586

Now that no scheme is required, we need to use the helper function to
include it, instead of the raw --host value. This does that.

Ref T595

We want to keep wf-cli service-agnostic and to make sure there's no
confusing overlap between this client and writeas-cli.

Ref T586

This automatically prepends https:// to any given --host value. It also
adds an --insecure flag, which will instead prepend http://

The goal with this is to save some typing and encourage operations over
HTTPS.

Ref T595

config.LoadUser was not ensuring the directory exists before trying to
load any already authenticated user, fixed using config.DirMustExist

config.LoadUser now only takes a *cli.Context

Particularly, in command descriptions.