squash! core/commands: Added 'log read' command

core/commands: Use a unidirectional channel for 'log read' output

refactor(core) extract http

PACKAGE DOCUMENTATION

package corehttp

    FUNCTIONS

    func GatewayOption(n *core.IpfsNode, mux *http.ServeMux) error

    func ListenAndServe(n *core.IpfsNode, addr ma.Multiaddr, options
    ...ServeOption) error

    func WebUIOption(n *core.IpfsNode, mux *http.ServeMux) error

    TYPES

    type ServeOption func(*core.IpfsNode, *http.ServeMux) error

    func DaemonOption(cctx commands.Context) ServeOption

Miscellaneous changes

The area above the lock was getting big. Moving this up to avoid
mistakes down the road.

closes #394 https://github.com/jbenet/go-ipfs/issues/394

initial implementation of repo-gc command

fix #424: when adding blocks, provide to exchange asynchronously

@jbenet

would like it to work this way

@jbenet

p2p/net/conn: only reuseport if avail

benchmark CLI `ipfs add`