Usage of diff and patch bindings

[sineemore]

I have several problems with diff and patch bindings:

• when comparing with empty string it reports one context line (empty string itself), but it probably should consider empty string as no input or provide a way to pass nil as empty input,
• it is not possible to specify (fake) filenames used in place of question marks in --- ? and +++ ?
• no way to pass context lines number,
• diff triggers if one of files doesn't exist, it is possible to fake such file with /dev/null, but it is platform dependent,
• binary files trigger utf8 conversion error, the overall behavior with binary files is yet blurry and it may not be related to bindings

Haven't used patch, but it seems that it works with strings, but not files and possibly requires to split combined diff first.

[naturallymitchell]

Ok.. We need patchutils' combinediff and splitdiff. I'm on it

[naturallymitchell]

and

• add null source to diff bindings #203
• allowing passing nil as empty input changeutils/diff-rs#4
• pass context lines number changeutils/diff-rs#5
• specify (fake) filenames used in place of question marks in --- ? and +++ ? changeutils/diff-rs#6

[naturallymitchell]

@sineemore how we doing on this? please check if those issues cover these items

[sineemore]

Mostly, I'll open related patch issues later.

I think I need to put somewhere my WIP on gut, so we can see which hacks were involved.