Read zipped word vectors

Currently the `-w` option allows specifying a word embedding file in text. However, these files may be quite large and are often saved in `.gz` format, for example. When given a compressed word embedding file, the program should still read it, unzipping it first.

Start by locating the command-line handling for the -w option and how it opens text word-embedding files. Check the existing input path and determine how a .gz embedding file should be accepted and decompressed; done means compressed word vectors load through -w just like uncompressed text files.

Written by the indexing model from the issue text.