Typed Lyra.insert method according to the schema used

[DanieleFedeli]

As per #14 (comment) this PR aims to type the insert method so the developer will know at compile time if the document inserted does not match the schema.

Code coverage:

File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
All files	87.95	72.82	90	89.04
src	84.68	66.07	84.61	85.2
errors.ts	82.6	100	50	75	8,20,23,26
levenshtein.ts	91.66	60	100	100	2-3
lyra.ts	93.69	78.78	100	94.54	118,155-158,173,184
stemmer.ts	30.76	18.18	100	30.76	22-23,28-49,56
tokenizer.ts	100	100	100	100
utils.ts	94.73	83.33	100	94.73	30
src/prefix-tree	95.55	83.33	100	97.7
node.ts	100	100	100	100
trie.ts	94.59	83.33	100	97.18	121,146

[micheleriva]

@DanieleFedeli thank you so much! I left a little comment, it would be if you'd be able to address it before merging 🙏

[micheleriva]

LGTM