Reverse multi-line diffs to standard order

[nylen]

Display multi-line diffs in the same standard order as diff, git, etc:

- actual / removed
+ expected / added

The current order is unintuitive which makes it harder to read at a glance:

+ expected / added
- actual / removed

Pending resolution of kpdecker/jsdiff#14 this works by reversing the added and removed strings passed to diff.createPatch, and then reversing the + and - status of each change.

[boneskull]

@nylen I don't understand what this has to do with jsdiff?

[boneskull]

@nylen does this depend on #1648 at all?

[nylen]

This is really a jsdiff issue but we can and should work around it here, since there doesn't seem to be a clean way to tell jsdiff to do this.

This and #1648 are both usability improvements to diffs, but they are independent changes.

[nylen]

@boneskull this PR and #1648 are big wins for diff usability, can they be merged please?

before:

after:

[nylen]

@a8m @boneskull @danielstjules @dasilvacontin @jbnicolai @pkozlowski-opensource @travisjeffery review please? I'd really like to get this (or something like it) merged. Same goes for #1648.

[nylen]

ONE MONTH LATER

Now that kpdecker/jsdiff#14 is fixed, this PR is obsolete. The correct fix is to upgrade to the newest version of jsdiff.

[danielstjules]

Awesome! And sorry for the delay! Glad it was fixed upstream, too, since I use it on other projects :)