Add option to ignore line endings and/or whitespace in a diff (BB-3879)

I just submitted a smallish change. The website shows it as a humongous change because it considers every line as edited.

Presumably this must be due to line endings in some way.

I propose that the website diff ignores differing line endings and just normalises them. Otherwise the diff is just not useful.

Here is an example.
https://bitbucket.org/Timwi/parsecs/changeset/65ffab8b8060#chg-Parser.cs