[new release] links, links-postgresql, links-sqlite3 and links-mysql (0.9.6)

CHANGES:

This release extends the core features of Links and resolves various
minor bugs.

* Links now supports System F-style explicit type abstractions:
For instance, writing `/\ [a, e::Row] { foo }` abstracts the expression `foo`
over type variable `a` and row variable `e`. Here, `foo` must have a unique
type and must be pure (to satisfy the value restriction).
* Fixed a bug in "mixing" query normalisation, which prevented certain queries using
concatenation inside `for` statements from being correctly converted to SQL.
* Links now has basic support for temporal database operations. More information
can be found on the [Wiki](https://github.com/links-lang/links/wiki/Temporal-Databases).
There are new keywords: `valid`, `to`, `vt_insert`, `tt_insert`, and `TemporalTable`.
* A new commandline option `--compile` (shorthand `-c`) has been
added, which runs Links in a "compile only" mode. In this mode the
JavaScript compilation artefact can be saved to a file (the naming
of this file is controlled via the commandline option `-o`). Note
that the generated file may not be directly runnable without linking
the runtime system first. Currently, the runtime system must be
linked manually.
* Fixed a bug where calling either of `newAP`, `newClientAP`, and
`newServerAP` on the client-side would crash the client.
* It is now possible to dispatch an MVU message from outside of the
event loop. This is particularly useful, for example, when dealing
with a persistent, stateful thread which is receiving messages from
a server. New things include:
+ A new type alias `MvuHandle(msg)`.
+ A family of runners: `runHandle`, `runCmdHandle`,
`runSimpleHandle` which return an `MvuHandle(msg)` rather than the
unit value.
+ A new dispatcher `Mvu.dispatch : (msg, MvuHandle(msg)) ~> ()`,
which directly dispatches a message to the MVU loop.

* The built-in webserver now supports SSL connections. To enable
secure connections, you must first obtain an adequate certificate
and key, e.g. via Let's Encrypt or a self-signed certificate. The
latter can be useful for testing, e.g. the following command starts
an interactive process to create a self-signed certificate (that
uses 4096 bits RSA encryption and is valid for 365 days):
```shell
openssl req -x509 -newkey rsa:4096 -keyout server.key -out server.crt -days 365 -nodes
```
After obtaining a valid certificate, you must tell Links to run in SSL
mode and you must also tell it how to locate the `key` and `crt`
file. This can be done via a configuration file, e.g.

```