release 0.15.1

[jeremyandrews]

• #374 renamed simple-with-session.rs to session.rs and simple-closure.rs to closure.rs to avoid confusion with the simple.rs example as they all do different things
• #385 properly configure --running-metrics VALUE when set manually
• #382 set client timeout to 60 seconds by default, used for all requests made; introduce --timeout VALUE where VALUE is seconds as integer or a float; timeout can be configured programatically using GooseDefault::Timeout
• #381 display requests per second graph on the HTML report