Support "+" character in file paths

[petethomas]

Adding a file that includes + characters in path can result in a stored path that uses spaces instead. For example:

const ipfsAPI = require('ipfs-api')
const ipfs = ipfsAPI()
ipfs.files.add(
  [{
    path: 'ti,c64x+megamod-pic.txt',
    content: Buffer.from('testing', 'utf-8')
  }],
  (err, res) => {
    if (err) done(err)
    console.log(res)
  }
)

Current result:

[ { path: 'ti,c64x megamod-pic.txt',
    hash: 'QmZJsQUWUes6vz6DzDT3z6383k1Y4hFYUKun9UkPN1PYSX',
    size: 15 } ]

Expected result:

[ { path: 'ti,c64x+megamod-pic.txt',
    hash: 'QmZJsQUWUes6vz6DzDT3z6383k1Y4hFYUKun9UkPN1PYSX',
    size: 15 } ]

Expected result preserves +s similar to the command-line utility. For example:

λ ipfs add -w ~/projects/linux/Documentation/devicetree/bindings/interrupt-controller/ti,c64x+megamod-pic.txt
added QmQ2eHGDMqC7dBD44EJFQRqkypPKQ9z9coBi1VX7vBZhPZ ti,c64x+megamod-pic.txt
added QmXdMfwwg4xrVVHo8YGwjbRChnM22UCs21r4zWFgmjeZKU
λ ipfs get QmXdMfwwg4xrVVHo8YGwjbRChnM22UCs21r4zWFgmjeZKU
Saving file(s) to QmXdMfwwg4xrVVHo8YGwjbRChnM22UCs21r4zWFgmjeZKU
 4.03 KB / 4.03 KB [============================================================================================================================================================================] 100.00% 0s
λ cd QmXdMfwwg4xrVVHo8YGwjbRChnM22UCs21r4zWFgmjeZKU/
λ ls
ti,c64x+megamod-pic.txt
λ

I think this package can achieve parity by URI-encoding the path before getting the file stream.

-pete