mailTemplate - Send an email using a PHP template file.
=======================================================

`mailTemplate($_filename, $_v)` causes the PHP engine to parse the PHP file specified by `$_filename`, with the
variables passed in the variable `$_v`, which should output an [RFC-822](https://tools.ietf.org/html/rfc822) (and its
[successors](https://en.wikipedia.org/wiki/Email#Message_format)) style message.
The function then extracts the headers from the message, grabs the "To" and "Subject" lines from it, and then passes
the "To:", "Subject:", message body, and remaining headers, to the PHP
[`mail()`](https://secure.php.net/manual/en/function.mail.php) function.

As an example, consider template file "thanks.php"

	To: <<?= $email ?>>
	Subject: Thank you for your request
	Content-Type: text/plain; charset=utf-8

	Dear <?= $name =>,

	Thankyou for your request, one of our staff will contact you <?= $when =>.
	<?php if ($important) { ?>

	Your request is important to us.
	<?php } ?>
   
Which could then be called with:

	mailTemplate("thanks.php", [
		'email' => "dave@example.com",
		'name' => "Dave",
		'when' => "tomorrow",
		'important' => FALSE,
	]};

Note that, as of this implementation, `$_filename` is read using
[`include()`](https://secure.php.net/manual/en/function.include.php), so it uses the file-finding rules defined therein.

Also, it is worth remembering that PHP eats newlines directly following a PHP close tag. Therefore, if you have:

	To: <?= $recipient ?>
	Subject: ...

Then the newline following the close tag will be eaten by the PHP parser, and you'll end up with:

	To: example@example.comSubject: ...

To work around this, you need to either make the closing tag not the last thing on the line (e.g. by adding a trailing
space to the line), or forcibly output a newline yourself from within the PHP, e.g.:

	To: <?= $recipient."\n" ?>
	Subject: ...