Allow 4+ spaces of indentation for image options

[jelmer]

Previously, this only supported 3.

[flying-sheep]

That doesn‘t work, this would wrongly accept the following:

.. image::
 :height: 1px

You need to use PEEK in some form. The current way this works is like this (<a/b/c> are placeholders for spaces, e.g. <a > is 4 spaces, <b> is 3 spaces, < c > is 9 spaces):

.. something::

<a >..<b>image::
<   c   >:height: 1px

1. after <a >, PEEK[..] is [\s\s\s\s]
2. after image::, PEEK[..] is [\s\s\s\s, \s\s\s] (indentation <a > and then the spaces after the “..” <b>)
3. after < c >, PEEK[..] is [\s\s\s\s, \s\s\s\s\s], because the PUSH(POP ~ " ") modified the last entry of the stack, adding 2 spaces.

so c contains the 4 spaces from the indentation <a >, and then the (3+2) spaces from the “..” and after.

[jelmer]

That doesn‘t work, this would wrongly accept the following:

.. image::
 :height: 1px

That's valid though? rst2html happily accepts this:

.. image:: foo.png
 :height: 1px

turning it into:

<img alt="foo.png" src="foo.png" style="height: 1px;" />

[flying-sheep]

Ugly but OK. Can you add a test like this that checks that it parses similar to the below? (doesn’t need to create a warning, we don’t support that yet)

.. pull-quote::
   .. image:: foo.png
 :height: 1px

❯ rst2pseudoxml image.rst
image.rst:3: (WARNING/2) Block quote ends without a blank line; unexpected unindent.
<document source="image.rst">
    <block_quote classes="pull-quote">
        <block_quote>
            <image uri="foo.png">
        <system_message level="2" line="3" source="image.rst" type="WARNING">
            <paragraph>
                Block quote ends without a blank line; unexpected unindent.
        <field_list>
            <field>
                <field_name>
                    height
                <field_body>
                    <paragraph>
                        1px