Lua output fixes

[Zash]

Fixes for some quirks noticed while working on #1810

• +.inf was not handled
• yq -o lua .foo <<< '{"foo":{"bar":1}} or the --prettyPrint flag would output {bar=1} only, without the pre- & suffix.
• Handle empty Tag field, if the parser side does not set it (I did before finding a good way to distinguish integer and float in the Lua parser)

Could split into multiple PRs if that is desirable.

[mikefarah]

Is it possible to add a test to show the prettyPrint fix? If it can't be done in lua_test.go you could always add it in as an acceptance tests shell file (under output_format.sh will probably do).

[Zash]

Will try.

[Zash]

Before

...
testLuaOutputPretty
ASSERT:expected:<return {
	["animals"] = {
		["cat"] = "meow";
	};
};> but was:<{
	["animals"] = {
		["cat"] = "meow";
	};
}>
shunit2:ERROR testLuaOutputPretty() returned non-zero return code.
testLuaOutputSubset
ASSERT:expected:<return {
	["cat"] = "meow";
};> but was:<{
	["cat"] = "meow";
}>
shunit2:ERROR testLuaOutputSubset() returned non-zero return code.

After

...
testLuaOutputPretty
testLuaOutputSubset

Ran 17 tests.

OK