Add a simple language model maker script

[lenzo-ka]

No description provided.

[dhdaines]

Ah, this is good, probably a lot of people would like to make a simple LM without having to install KenLM or some other package with more onerous requirements. I will try it out / test it tomorrow. Thanks!

[lenzo-ka]

Any thoughts on this @dhdaines ?

[dhdaines]

Ah, yes! The day I thought I would spend catching up PocketSphinx stuff I spent ... doing something else (probably parsing PDFs). It does look good, I promise I will approve/merge it soon!

[dhdaines]

Just made a couple of tweaks to this - at the very least it should do something helpful when called with no arguments, so I changed that, and made use of argparse.FileType so you can call it with --sentfile - to get input from standard input. Also ran black and isort on the code for consistent formatting.