Limit length of slug

[h4cc]

Provide a way to limit the length, with and without breaking inside a slugged word.

[fahrradflucht]

I tried to implement this but, I just read that you wrote:

with and without breaking inside a slugged word.

My implementation atm only does the latter.

That aside I came here to ask whether I should bump the Elixir version (like I did) and use to_charlist or if I should use to_char_list which is soft-deprecated since 1.3.0 to maintain support for 1.0 (I don't actually know in which version to_charlist has been implemented but it isn't there in 1.0 and it's there in 1.3).

Edit: Now that I think about it, bumping the Elixir version should probably include bumping it in .travis.yml

[fahrradflucht]

I have done a second commit on my branch that adds an option to handle both cases (with or without breaking inside a slugged word) and cleans the whole thing up a bit.

Now a primarily need feedback regarding that Elixir version/to_charlist thing.

[h4cc]

I added some tests that show some behaviour that might not be intended:

    assert Slugger.truncate_slug("a-b-c", 10) == "a-b-c"
    assert Slugger.truncate_slug("a-b-c", 5) == "a-b-c"
    assert Slugger.truncate_slug("a-b-c", 4) == "a-b"
    assert Slugger.truncate_slug("a-b-c", 3) == "a-b"
    assert Slugger.truncate_slug("a-b-c", 2) == "a"
    assert Slugger.truncate_slug("a-b-c", 1) == "a"
    assert Slugger.truncate_slug("a-b-c", 0) == ""
    assert Slugger.truncate_slug("a-b-c", -1) == "c"
    assert Slugger.truncate_slug("a-b-c", -2) == ""
    assert Slugger.truncate_slug("a-b-c", -3) == ""
    assert Slugger.truncate_slug("a-b-c", -4) == "b"
    assert Slugger.truncate_slug("a-b-c", -5) == "-b"

I assume that max_length < 1 should be "".