Big table.tostring() overhaul: removed some dead cruft (new_indent...) and added...

Big table.tostring() overhaul: removed some dead cruft (new_indent...) and added some features: (1) option "notag" gets "tag" field to be treated as a regular field, i.e. tables are printed the Lua way, rather than the "`Sometag{ ... }" Metalua way; (2) option "indentN" with N a number will indent tables by a fixed amount of N spaces, instead of aligning siblings together; if N is omitted, it defaults to 3.