docs: enhance query options, instance type, and toJSON() result type

[cyjake]

also fixes return type of compound queries such as:

const posts  = await Post.where({ title: { $like: '%a' } }).select('title');
assert.equal(posts.length, 3);

[codecov-commenter]

Codecov Report

Merging #207 (3cc929a) into master (8d30a9a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #207   +/-   ##
=======================================
  Coverage   97.17%   97.17%           
=======================================
  Files          42       42           
  Lines        3049     3049           
=======================================
  Hits         2963     2963           
  Misses         86       86           

Impacted Files	Coverage Δ
src/drivers/sqlite/index.js	100.00% <ø> (ø)

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