Disallow parsing 0 as season number

Fixes #14.

Add keywords: EAC3, E-AC-3, Hardsubs, HEVC2, Hi444, Hi444P, Hi444PP

Fix invalid reference

Since c3ece46, Elements::get no longer returns a reference.

Update readme

Improve volume prefix detection

It worked for "Vol.01" (two tokens) but not "Vol.1" (one token).

Fix compilation error in VS 2015

Fixes #2.

Don't always identify enclosed words

Add keywords: OAD, Special, Specials

There are a few anime titles such as "Special A" that are going to be miscategorized, but the addition of the keywords provide greater benefits.