Luacheck suggestions

[bjornbm]

This first commit avoid shadowing variables, ref #8 (comment)

Luacheck reports a number of other things. Removing trailing whitespace is one, but I agree with you that it is not important (and the suggestion can be disabled).

Complaining about globals #10 is another one.

Another one, which I think is quite meaningful as it can catch a mismatch between intent and behavior, is reporting unused variables or arguments. Some examples:

ple.lua:561:9: unused variable ci
ple.lua:723:6: unused loop variable i
ple.lua:768:23: unused argument b 

For the first two, the idea would be to replace the binding to ci or i with bindings to _ which I understand is the convention to say explicitly that you are not interested in the value (as opposed to not using it due to a typo or other mistake in later code). For example, line 561 would become:

		local _, cj = b:getcur()

line 723:

	for _, bx in ipairs(editor.buflist) do

For line 768 (and several similar ones), I understand it the function will likely be called with the current buffer b (from a key binding), but the b is not used. I could understand why you might want to keep the argument to show the expected way it will be called.

function e.nextbuffer(b)
	-- switch to next buffer
	local bln = #editor.buflist
	editor.bufindex = editor.bufindex % bln + 1
	editor.buf = editor.buflist[editor.bufindex]
	editor.fullredisplay()
end--nextbuffer

In any case, if you are interested I can push more commits for things like the unused variables.

Note that I haven't run luacheck over pleterm.lua or buffer.lua. I thought it best to limit to ple.lua until I know what may interest you in terms of pull requests.