HMRC Manuals have a custom prefix

As the HMRC manuals are not general government guidance on tax and benefits,
the agreement is that they should be treated as a special case.
HMRC Manuals have a custom title tag
Add a component to title tag for normal manuals

This makes it more consistent with GOV.UK, especially content from Whitehall
which includes the format/category in the title.
Merge pull request #110 from alphagov/hmrc_manuals_have_custom_prefix

HMRC manuals have custom prefix