feat: add --expand-opt flag

[numToStr]

If this flag is provided, then ? (optional) will expand to nil|type. As ? is only allowed for ---@field and ---@param, thus this will only affect the vimdoc rendering of classes and functions.

local M = {}

---@class HelloWorld
---@field message? string First message to the world
---@field private opts? table
---@field secret table Sauce

---Prints given value
---@param message string
---@param opts? table
function M.echo(message, opts)
    return print(message)
end

return M

• Without --expand-opt

HelloWorld                                                          *HelloWorld*

    Fields: ~
        {message?}  (string)  First message to the world
        {secret}    (table)   Sauce


M.echo({message}, {opts?})                                              *M.echo*
    Prints given value

    Parameters: ~
        {message}  (string)
        {opts?}    (table)

• With --expand-opt (notice the nil)

HelloWorld                                                          *HelloWorld*

    Fields: ~
        {message}  (nil|string)  First message to the world
        {secret}   (table)       Sauce


M.echo({message}, {opts?})                                              *M.echo*
    Prints given value

    Parameters: ~
        {message}  (string)
        {opts}     (nil|table)

Resolves #44