Log Message:
fzf: Use `do-install' to install only needed files

lang/go/go-package.mk install several files that are not needed for packages
that just install a program. Define `do-install' target to avoid that.

While here also install fzf-tmux in bin/, man pages under ${PKGMANDIR}
accordingly and shell completions/bindings and vim plugin under
share/fzf.  Update MESSAGE to reflect this change.

PKGREVISION++

Discussed with <maya>.