tail: fix event filter

could not receive event of files in a same directory, receive only event
added at first.
test: read the rest after removing
tail: fix first line counting

and Lookup() return value
tail: add Tail.Clone()

shares lines but rewind current element to head
tail: integrate TailName and Tail

then create Tail interface.
tail: rework filter

using interface
tail: fix empty line handling
lotfd: add simple network services

just telneting specified port
pkg: ignore binary
doc: add README, update