Add streams and directory building

[travisperson]

This PR adds stream support for any command send data through the files argument of send. It addresses issue #4 and #3.

Appropriate values for any files argument are streams, vinyl files, or buffers. Any stream or buffer will be converted to a vinyl file with the cwd, base, and path set to /, which basically is just an unnamed file.

The base of any filename is the relative pathing from the vinyl file base.

Wrapped files in a directory

files.push(new File({
    base: '/',
    path: '/base/dir/hello.txt',
    contents: new Buffer("world")
}))

files.push(new File({
    base: '/',
    path: '/base/dir/ipfs.txt',
    contents: new Buffer("is cool")
}))

files.push(new File({
    base: '/',
    path: '/base/readme.md',
    contents: new Buffer("wow")
}))

files.push(new File({
    base: '/',
    path: '/base/dir/other/readme.md',
    contents: new Buffer("wow")
}))

{
  "Name": "base/readme.md",
  "Hash": "QmbxMp5x7RbqHSTrrKQCYjccw2obvgcz2GEyz3gEkixhDS"
}
{
  "Name": "base/dir/hello.txt",
  "Hash": "QmNyJpQkU1cEkBwMDhDNFstr42q55mqG5GE5Mgwug4xyGk"
}
{
  "Name": "base/dir/ipfs.txt",
  "Hash": "QmfBfWxn32sGXbkgDoeNLT5rBcTehYffMyeU5LFTTByt6V"
}
{
  "Name": "base/dir/other/readme.md",
  "Hash": "QmbxMp5x7RbqHSTrrKQCYjccw2obvgcz2GEyz3gEkixhDS"
}
{
  "Name": "base/dir/other",
  "Hash": "QmSV3qfAxjMTdGrB5tGA4daPsL6NoZKxhUx6QxCfqLCeGp"
}
{
  "Name": "base/dir",
  "Hash": "QmeE8ZjMwexLbZBAX1dxwguCaQ5xyHw4wYGmGiyfzEqL2p"
}
{
  "Name": "base",
  "Hash": "QmeUg1UYEAmrZZWW7URFZXMYMVECzfmgdgke95F8HqauLz"
}

Grouping of files

files.push(new File({
    base: '/base/',
    path: '/base/dir/hello.txt',
    contents: new Buffer("world")
}))

files.push(new File({
    base: '/base/',
    path: '/base/dir/ipfs.txt',
    contents: new Buffer("is cool")
}))

files.push(new File({
    base: '/base/',
    path: '/base/readme.md',
    contents: new Buffer("wow")
}))

files.push(new File({
    base: '/base/',
    path: '/base/dir/other/readme.md',
    contents: new Buffer("wow")
}))

{
  "Name": "readme.md",
  "Hash": "QmbxMp5x7RbqHSTrrKQCYjccw2obvgcz2GEyz3gEkixhDS"
}
{
  "Name": "dir/hello.txt",
  "Hash": "QmNyJpQkU1cEkBwMDhDNFstr42q55mqG5GE5Mgwug4xyGk"
}
{
  "Name": "dir/ipfs.txt",
  "Hash": "QmfBfWxn32sGXbkgDoeNLT5rBcTehYffMyeU5LFTTByt6V"
}
{
  "Name": "dir/other/readme.md",
  "Hash": "QmbxMp5x7RbqHSTrrKQCYjccw2obvgcz2GEyz3gEkixhDS"
}
{
  "Name": "dir/other",
  "Hash": "QmSV3qfAxjMTdGrB5tGA4daPsL6NoZKxhUx6QxCfqLCeGp"
}
{
  "Name": "dir",
  "Hash": "QmeE8ZjMwexLbZBAX1dxwguCaQ5xyHw4wYGmGiyfzEqL2p"
}

*Note: this is slight different from what was shown in #3.

[jbenet]

LGTM -- @krl @mappum ?

[krl]

cool, looking good