:sparkles: index access

[kkharji]

Purpose

Make it possible to access sqlite.tbl operations using index access:

for example:

local kvtable = tbl("kvtable", {
  key = { "text", primary = true, required = true, unique = true },
  value = "integer",
}, db)

--- access/insert-to/remove using primary key
kvtable.a = { value = 1 }
kvtable.a = nil
--- access/update a row field value 
kvtable.a.value = 2
kvtable.a.value = nil
--- sets a key field value without creating the key first
kvtable["some key with spaces :D"].value = 4

closes #98

[kkharji]

... to be continued sometime next week. reviews are welcomed.