Sort out behaviour of newlineIsToken and ignoreWhitespace

[ExplodingCabbage]

Three fixes here:

• ignoreWhitespace now behaves the same as other ignoreXxx methods - i.e. changes how tokens are compared for equality but does NOT affect the values that show up in the returned change objects. Resolves https://github.com/kpdecker/jsdiff/pull/219.
• Fix the incompatibility between newlineIsToken and ignoreWhitespace. Resolves https://github.com/kpdecker/jsdiff/issues/472, albeit not quite in the way I'd originally intended.
• I've undocumented diffTrimmedLines. I don't see a reason to have two ways (diffTrimmedLines & ignoreWhitespace) to do exactly the same thing, so I've purged one from the documented API. (I'll still keep the method itself around just for backwards compat, though.)

For me to do before merging:

• [x] Sanity check this works at all
• [x] Add release notes. Remember to call out the deprecation of diffTrimmedLines.
• [x] Take another look at https://github.com/kpdecker/jsdiff/pull/219. (I didn't read the diff there before doing my own work on this - I'd actually forgotten @Mingun had actually put up a PR about this and not just an issue.)
• [x] Update the failing tests
• [x] Add a new test confirming compatibility between newlineIsToken and ignoreWhitespace.

[ExplodingCabbage]

@Mingun I'd welcome any comments you have on this. Have I failed to properly handle anything here that your PR did better?

[Mingun]

Hi @ExplodingCabbage!

My intention was to get correct diff behavior that you usually expect from code diffs. When I implemented my fix in #219 I think, I got the expected results, that TortoiseGitMerge and similar tools give you when you merge file in ignored whitespace mode. I probably didn't actually investigate that behavior is identical, but I remember that at least results was not surprising:

• removed lines keeps formatting from "old" chunk (there is anyway no "new" chunk)
• added lines keeps formatting from "new" chunk (there is anyway no "old" chunk)
• don't remember what was returned for changed lines

Anyway, I think, that your fix is simpler, but I suggest to take tests from my PR, because they:

• shows all possible scenarios of space and newline combinations https://github.com/kpdecker/jsdiff/pull/219/files#diff-f6880fa6bc33ccb261ba2f8f22c2c97c990b0cbc56e64085d88b76d08d1c8de2R67-R85
• shows one relatively real-life scenario https://github.com/kpdecker/jsdiff/pull/219/files#diff-f6880fa6bc33ccb261ba2f8f22c2c97c990b0cbc56e64085d88b76d08d1c8de2R88-R106

I think, that having them it is much better to understand what to expect from results.