Updates for wakepy 0.8.0: Docs + small enhancements

[fohrloop]

Went through the public API parts of wakepy for the 0.8.0 release, and
updated the API Reference documentation. While fixing the docs, found
and fixed few other additional things.

Docs

• Add Method, ActivationResult, MethodActivationResult, ActivationError,
  MethodExit and PlatformName to API Reference.
• Add a lot of more cross-linking in the API Reference.
• Link colors: links to darker blue, inline code from fuchsia to
  brownish red.
• List items paragraphs: Remove extra space from above, and add some
  space below.

Method

• Remove .description attribute. Was never used anywhere.
• supported_platforms: Made any Method by default to support any
  platforms. This is therefore used as a whitelist. The person
  subclassing Method may then either use the automatic platform
  support check (with supported_platforms), or implement caniuse(), or
  just let the code crash on unsupported systems, which will be then
  handled and the method would be marked as failing one.

Naming: mode_name

• Use mode_name and method_name consistently everywhere
• Rename: Method.mode -> Method.mode_name. Makes it easier to
  differentiate if talking about Mode instance or a string.
• Rename the Mode.from_name parameter modename to mode_name
• Rename: ActivationResult.modename -> .mode_name
• Add: MethodActivationResult.mode_name

Dbus Adapter

• Make the wakepy.dbus_adapters.jeepney.JeepneyDBusAdapter importable
  from wakepy.JeepneyDBusAdapter using lazy-loading from PEP-562.