Error messages should be sentence fragments, and therefore:
1. Should not begin with a capital letter,
2. Should not conclude with punctuation, and
3. Should not end a sentence and begin a new one
Move the delta application functions into `delta.c`, next to the
similar delta creation functions. Make the `git__delta_apply`
functions adhere to other naming and parameter style within the
library.
Make our overflow checking look more like gcc and clang's, so that
we can substitute it out with the compiler instrinsics on platforms
that support it. This means dropping the ability to pass `NULL` as
an out parameter.
As a result, the macros also get updated to reflect this as well.
