Make rel() and loc() return default values if no argument is passed

[Aeryle]

Current behavior of relative and local function:

relative()        // Expected at least 1 arguments, but got 0.
relative(0)       // '~'
relative(0, 0, 0) // ['~', '~', '~']

local()           // Expected at least 1 arguments, but got 0.
local(0)          // '^'
local(0, 0, 0)    // ['^', '^', '^']

New behavior:

relative()         // ['~', '~', '~']
relative(0)        // '~'
relative(0, 0, 0)  // ['~', '~', '~']

local()            // ['^', '^', '^']
local(0)           // '^'
local(0, 0, 0)     // ['^', '^', '^']

With this PR, relative() and local() is the same as doing relative(0, 0, 0) and local(0, 0, 0).

Tell me if you see anything to improve.

You can test this PR using npm i aeryle/sandstone