docs: html.in: Convert api to rst

docs: html.in: Convert api to rst

There were a number of occurrences where we used nested inline markup
(verbatim + refs) which is currently not possible with RST syntax [1].
There is a possible workaround involving substitution definitions like

  .. |virConnectPtr| replace:: ``virConnectPtr``
  .. _virConnectPtr: /html/libvirt-libvirt-host.html#virConnectPtr

Substitutions cannot be made generic, hence we cannot create a template
for substitution and use a single template everywhere, so we'd end up
with a lot of clutter and convolution. Therefore, we can make an
exception and just link the data type without further style markup.

[1] https://docutils.sourceforge.io/FAQ.html#is-nested-inline-markup-possible

Signed-off-by: Erik Skultety <eskultet@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>