feat: add more tests and parse hunks a little differently

[wolfv]

One of the test files (0001-cross.patch) had an issue because empty whitespace lines are removed.

However, the old parser was looking for +, - and to add a line to the hunk.

With this modification, we try parsing until we find a next header and also take into account empty whitespace lines as context.

It will still fail on the example mentioned:

--- main.c
+++ main.c
@@ -1,4 +1,7 @@
+#include<stdio.h>
+
 int main() {
 double a;
--- a;
+++ a;
+printf("%d\n", a);
 }

Where the --- a; is interpreted as a "header".

I tried a little bit to add range counting to the parser so that this case would also be fixed but I didn't finish that yet. I think it should be doable though :)

[vrmiguel]

Awesome stuff, @wolfv!

Really sorry for the delay