[docs] Add Sphinx-based documentation (not built by default)
[api] DBusInterface: Rename destination to service

This aligns better with "DBusAdaptor". We keep a (deprecated and
undocumented) alias "destination" working, so legacy code written
against the old API doesn't break.
[api] DBus: Merge BusType enums to single enum in "DBus" QML object

The BusType is used in both DBusAdaptor and DBusInterface, so move
the enum to a common class (DeclarativeDBus, aka "DBus" in QML).

Keep the old BusType enums around (but undocumented + deprecated)
to not break existing code.
[api] DBusInterface, DBusAdaptor: Rename busType to bus
[compat] Bump import version to 2.0, legacy aliases in subclasses

Import version 1.0 will expose the compatibility aliases for old names
of properties (and enums), whereas import version 2.0 will have the
clean new API without any compatibility aliases.
[api] DBusInterface: Reduce number of API calls (combined functions)

Merge typedCallWithReturn into typedCall
Merge emitSignalWithArguments into emitSignal
[api] DBusInterface: Implement setProperty
[api] Version 2.0 API with deprecated fields removed
[signals] Document signal handling, easier name mangling
[docs] Simplify and clarify signal name matching
Merge pull request #21 from thp/docs

API cleanup (import version 2.0), Sphinx-based documentation (not built by default)