Ngram tokenizer for sqlite3 fts5

This tokenizer works behind another tokenizer like unicode61 (default).

Example:

const sqlite = require('better-sqlite3');
const tokenizer = require('sqlite3-ngram-tokenizer');

const db = sqlite(':memory:');
db.loadExtension(tokenizer.pluginPath); // pluginPath does not contain extension

db.exec(`
CREATE VIRTUAL TABLE t1 USING fts5(x, tokenize = 'ngram');
`);

It tokenizes latin words by 2-gram with seperate first letter: "letter" => [l le et tt te er], so it will match "let" but not "etter".

For non-latin words, it tokenizes them by 1-gram. It performs like String.includes() on non-latin words.

You can specify other tokenizers like

-- porter tokenizer also works behind another tokenizer
CREATE VIRTUAL TABLE t1 USING fts5(x, tokenize = 'ngram porter unicode61 remove_diacritics 1');

NOTICE

highlight() may not work as expected behind a porter tokenizer.