Refactor argument parsing

[atticus-sullivan]

Like noted in #20 the current argument parsing is not as clean as I like it to be.

C.f.

cluttealtex/src_teal/texrunner/option.tl

Lines 55 to 65 in ea1626a

	if opt.param then
	if param then
	-- --option=param
	else
	if opt.default ~= nil then
	-- no param with space if option specifies a
	-- default in order to avoid accidentally
	-- consuming the next argument
	param = opt.default
	else
	-- --option param

We should refactor/rewrite this.

Note: It's important that --option0 --option1 or also --option0 file.tex is still possible even if --option0 has a default value. If that's not possible we should consider disabling passing parameters this way (only via = possible then) or maybe even move the whole configuration to the config file (#16) eventually (but I'd prefer to still have commandline options).

[atticus-sullivan]

Also remember to

• put more comments in the code
• think about splitting up large functions into smaller more manageable ones -> we can write more tests then

[atticus-sullivan]

Already done in #17