v0.2.0-alpha.2

Added

• Phlex views for hanami-mailer. A mailer renders the Phlex class whose container key matches its own, so
  MyApp::Mailers::Welcome renders MyApp::Views::Mailers::Welcome with no configuration.
• Phlex::Hanami::Mailer::View and Phlex::Hanami::Mailer::Layout, and Phlex::Hanami::Mailer::Renderable for an
  existing Phlex::HTML base class.
• A plain text alternative part, converted from the rendered HTML by Phlex::Hanami::Mailer::Text. Override
  text_body on the view to write it by hand.
• A mail layout convention: Views::Mailers::Layout in a slice wraps that slice's mail views.
• Usage documentation under docs/usage, covering views, layouts, the view context,
  helpers, mailers and how the gem hooks into Hanami.
• Phlex::Hanami::MailerViewError, raised when a mailer is paired with a Phlex view that is not a mail view,
  rather than sending a message whose plain text part is markup.

Changed

• url in a view returns a String. Hanami's routes helper returns a URI, which Phlex rejects as an attribute
  value, so a(href: url(:posts)) raised.

Fixed

• path in a mail view raises Phlex::Hanami::RelativePathError instead of writing a relative link an email client
  cannot follow.