widgets: add webkit context object to wkline struct
widgets/volume: implement JSCore onDataChanged callback

Ref #20
Merge branch 'develop' into feature/jscore

Conflicts:
	src/widgets/volume.c
	src/wkline.h
Revert "main: use "screen" instead of "monitor" to be consistent"

This reverts commit a4f1f3c91731b36d33c2e9b9719a996abd12cb5b.

Conflicts:
	config.json
	docs/wkline.1
	src/wkline.c
Revert "widgets/xcb: use screen number from config"

This reverts commit f5a9967b796e69eb10d7867df68eb469fec83064.

Conflicts:
	src/widgets/desktops.c
	src/widgets/window_title.c
Fix screen -> monitor in wkline.c
Merge branch 'fix/revert-screen-monitor' into develop

Ref #4
main: exit if invalid monitor index is specified

Ref #4
main: goto config_err on invalid monitor index
Update project description
docs: add install docs
docs: add asciidoc man pages
docs: update man pages
docs: replace readme with asciidoc man page
docs: update filetype of asciidoc sources
Merge branch 'feature/update-docs' into develop
Merge branch 'develop' into feature/jscore
widgets: refactor jscore functionality
widgets: refactor to run data callback in main thread
widgets: use widget_data_callback for sending data