Rename `Substitution` to `Splice`?

[emhoracek]

One of the most confusing things about Heist is the difference between a "Splice" and "Splices". So, one of my favorite things about Larceny is that it makes the difference really clear -- a "Fill" (Heist's "Splice") is how you fill in a Blank, and a "Substitution" is a mapping from Blanks to Fills.

The only problem is, "Substitution" is a mouthful. It's annoying to say and to type. I end up missing "Splice", which is short and easy to spell and to say. It conveys the same meaning as well.

This would be a very breaking change.

[emhoracek]

Hmm I could just leave Substitution and add a deprecation warning...