Hashtag linking improvements

Also, add static pages

Including the `-d` flag ensures the package doesn't build. We need this
because it will immediately fail, since the static assets haven't been
compiled yet.

...instead of using os.Exit(). This makes it more apparent what's going
on, less error-prone, and more consistent with other command logic paths.

...instead of doing os.Exit(). This allows the func to be used in many
places (as it is) and handle success results in different ways.

Previously, this caused the single-user configuration process to exit
prematurely. This fixes that and closes #71.

use font-display:optional to optimize web font loading

This includes the appmigrations table in the schema files, and inserts
the current database version when running writefreely --init-db

Note the step is only required for multi-user instances.

Support user invites

This makes --gen-keys respect the keys_parent_dir config value

This logs the actual error when it occurs, instead of always saying that
the key already exists.

Support configuring resource directories

This adds new configuration values that specify the parent directory of
application resources:

- templates_parent_dir
- static_parent_dir
- pages_parent_dir
- keys_parent_dir

For any values not specified, the application will default to the
current directory.

This closes T560

This includes:

- A new `user_invites` config value that determines who can generate
  invite links
- A new page for generating invite links, with new user navigation link
- A new /invite/ path that allows anyone to sign up via unique invite
  link, even if registrations are closed
- Tracking who (of registered users) has been invited by whom

It requires an updated database with `writefreely --migrate` in order to
work.

This closes T556

This runs database migrations and obviates the need for manually running
changes.

Ref T509

Deploy the app in the proper dir for dependency management

Along with a recent change to how spaces are output by the
writeas/saturday library, this alters the CSS to make sublists display
correctly, and fixes #27.

This fixes the --config step so that when setting up a single-user
instance for the first time (and creating the admin user as part of the
process), the database is automatically initialized before creating that
user.

This removes the need for the --init-db command after --config when
setting up single-user instances.

It fixes #59: "no such table: users" error during the --config step on
single-user instances that haven't previously run --init-db.

This fixes the page not rendering on Windows.

Closes #61

Supports creating a build without SQLite support compiled in.

Previously the query would fail with "no such function: NOW"

Closes #56

SQLite doesn't have an `RLIKE` function, so the query for hashtagged
posts was failing before. This adds a `regexp` function to SQLite and
correctly retrieves all posts on a blog with the requested hashtag.

This closes #55

This avoids reading from the database after a transaction has been
started in CreateUser(), fixing the deadlock that occurred before.

Closes #53

Only check for username and password if driver type is mysql