fix(mode): incompatible with vim.v.count

[Iron-E]

Closes #25

v:count can't be updated manually, so I've created an alternate facility which tracks count until commands are executed:

local my_mode = {
	g = function()
		vim.notify('count: ' .. vim.g.myModeModeCount)
	end
}

vim.keymap.set('n', 'M', function()
	require('libmodal').mode.enter('My mode', my_mode)
end)