Add lzip support

[sorairolake]

Closes #400

[mholt]

Nice, thank you! This is looking good. Will merge this shortly. Appreciate your contribution!

[mholt]

Hm, lz4 compression with extension is failing. @sorairolake Does it fail for you locally?

[sorairolake]

@mholt Just now, I ran the test locally 10 times, 8 passed but 2 failed. I don't know why the test sometimes fails.

[mholt]

Hmm, sounds like something funky with the test suite. I'll look into it, but your change seems sound.

[sorairolake]

Both lz4 and lzip starts with "lz". So I think this may be related.

[mholt]

Ah, indeed -- make this comparison more strict and that should hopefully fix the test.

[sorairolake]

I think this can be fixed with the following changes:

Suggested change

	if strings.Contains(strings.ToLower(filename), lz.Name()) {
	if filepath.Ext(strings.ToLower(filename)) == lz.Name() {

However, this requires that the extension be the last element of the path.

[mholt]

That would fail for those cases as you say, but maybe a check for both a suffix of .lz or the string contains .lz.?

[sorairolake]

I think there is almost no possibility that .lz and .lz4 exists anywhere other than at the end of the path.

I think /path/to/foo.tar.lz or bar.7z.lz4 are possible, but /path/to/foo.lz.tar or bar.lz4.7z are almost impossible.

[mholt]

That's a good point.

[mholt]

Why was this one changed?

[sorairolake]

I thought this would be a conflict, but it was a misunderstanding. So I restored this.

[mholt]

Awesome, looks good now :) Thank you!

[mholt]

PS. I hope to travel to Japan someday :D