v0.16

Changelog

2b44b46 Add volume button/slider (resolves #20)
d9f1357 Fix cleanup when connection lost (resolves #26, #28)
9a05a38 Fix queue selection being reset on right click (resolves #21)
aaab2a3 Option for showing/hiding library toolbar (resolves #23)
553193e Update to latest gompd (2.2.0), gotk3 (0.5.2) (hopefully resolves #27); go 1.15+