Version bump to 0.4.0
Version bump to 0.4.0

Includes:

* changes to README inc documentation for Mustache
* propositional navigation
* simplification of kerning for logo
* optimisation of images

jonheslop/govuk_template,quis/govuk_template,froddd/govuk_template,jonheslop/govuk_template,daveraine/govuk_template,robinwhittleton/govuk_template,daveraine/govuk_template,jonheslop/govuk_template,alphagov/govuk_template,quis/govuk_template,bitzesty/govuk_template,alphagov/govuk_template,robinwhittleton/govuk_template,daveraine/govuk_template,robinwhittleton/govuk_template,froddd/govuk_template,froddd/govuk_template,alphagov/govuk_template,bitzesty/govuk_template,froddd/govuk_template,robinwhittleton/govuk_template,daveraine/govuk_template,alphagov/govuk_template,robinwhittleton/govuk_template,froddd/govuk_template,jonheslop/govuk_template,jonheslop/govuk_template,quis/govuk_template,bitzesty/govuk_template,alphagov/govuk_template,quis/govuk_template,quis/govuk_template