Add titleize Liquid filter

[jaredcwhite]

Like the docs say: a Liquid filter to transform a lowercase string, slug, or identifier string into a capitalized title. Uses the already present Utils.titleize_slug method.

input: {{ "to-kill-a-mockingbird" | titleize }}
output: To Kill A Mockingbird

[westonganger]

I dont like that this method converts dashes to spaces. I think that is undesirable for a general titleize method.

[jaredcwhite]

@westonganger Well that's how titleize works currently in ActiveSupport which we're hoping to integrate more of per #31, and it's also how Jekyll has worked in the past. Were you looking for something that only coverts underscores to spaces?

[westonganger]

After considering further hyphenated words are rarely necessary. Might as well stick to the convention.