Performance issues on large files

[oakmac]

I noticed some poor performance when using this extension on large files. For some files the extension is basically unusable due to how long it takes to process.

When I was developing atom-parinfer, I tested against cljs.core - which has over 10k lines. Had to come up with some performance hacks to improve Parinfer performance for that threshold.

Mainly:

1. Only sending the code that had likely changed to Parinfer instead of the whole file. See: this code as well as Issue #9
2. The use of a small LRU cache to prevent repeated processing.

I'm not sure these are perfect solutions and @shaunlebron has expressed improving performance in the main Parinfer algorithm, but these tricks might be helpful in the meantime.

[oakmac]

Since this issue was opened, parinfer.js has been re-written and is substantially faster than the implementation currently being used for this plugin.

atom-parinfer still uses the "parent expression" performance hack described here, although to be honest I'm not sure this is even necessary anymore. Either way, there have been zero complaints from users about speed issues.

FYI

[shaunlebron]

fixed by #10