updated readme, makefile
README: markdown and more info
version from git describe
README: electron environment hack
maintenance: use constants where possible
--fork option, usage info in README
add VFLAGS to makefile (-g for debug)
emit StatusNotifierHostRegistered
context menu on right click
icon updates; activate on activate
move watching to watcher; stop watching when vanished
remove posix dependency, lessen bad logging
show and unshow pixbuf icons