window: use readline for handling line input
help: add description of 'set volume' action
window: disable readline default autocompletion
window: read_key: move cursor back to position it was at before helper function call
actions: reset highlight position of main playlist when cleared
window: read_key: move cursor back to position it was at before callbacks were called
Merge branch 'master' of git://repo.or.cz/ncmpcpp