axel: patches new features added since version 2.4

- Displays awesome progress bar using unicode characters `-u` or
`--unicode` (config file option `unicode_output=1`)

- Implements something silimar to [dynamic segmentation](http://www.internetdownloadmanager.com/support/segmentation.html)

- Skip files that are already downloaded (don't clobber from wget) `-c`
or `--no-clobber` (config file option `no_clobber=1`)

- Recognize `Content-disposition` in HTTP headers, and save with
appropriate filename.

Moe info: https://gist.github.com/denji/6652068