Excel and quotation mark handling

This is kind of a follow up on #176

When pasting data from excel with quotation marks, this isn't handled properly by jExcel. After some testing, I found that excel has surprisingly complicated quote handling icw copy/paste.
Consider this excel table:

Copying it to a text file results in this (see image for whitespace characters):

copy pastable:

"single quote	1
ends with quote"	2
"surrounded by quotes"	3
no quote	4
"has a 	tab"	5
"a "" and a 	tab"	6
"""starts with quote, and has a 	tab"	7

If a cell has a tab, then it gets surrounding quotes. If there is also a quote in the cell, then that is escaped by doubling it. So how can excel know the difference between a cell that has quotes in the content or that is surrounded by quotes? Well, apparently it doesn't. When the text is copied back to excel, the surrounded by quotes cell loses the quotes. Also the first two cells are merged:

Copying it back to text results in

"single quote	1
ends with quote"	2
surrounded by quotes	3
no quote	4
"has a 	tab"	5
"a "" and a 	tab"	6
"""starts with quote, and has a 	tab"	7

All this is to say that there is probably no way to do it completely right, but as jExcel just interprets all quotes as cell delimiters (as far as I can tell) it can surely be improved

Start by reproducing the Excel copy/paste examples in the issue and compare how jExcel parses tabs, surrounding quotes, and doubled quotes. Trace the paste-handling entry point responsible for converting clipboard text into cells. Done means the examples are parsed more accurately, with behavior documented for cases Excel cannot distinguish.