v0.15.0

Added

• Add autocorrelation MCMCObserver
• add build methods to observers to make Arc<RwLock<Self>>s out of them

Fixed

• change build signature for standalone structs
• correct autocorrelation calculation

Other

• add usage doctest for AutocorrelationObserver
• update example with IAT observer and proper burn-in, as well as an IAT plot
• remove methods to set all observers and change the signature of with_observer to accept an Arc<RwLock<Observer>>
• switch Observer/MCMCObserver callback notation to terminate if true is returned