This adds `git_diff_buffers` and `git_patch_from_buffers`. This
also includes a bunch of internal refactoring to increase the
shared code between these functions and the blob-to-blob and
blob-to-buffer APIs, as well as some higher level assert helpers
in the tests to also remove redundancy.
It's hard or even impossible to correctly free the string buffer
allocated by git_patch_to_str in some circumstances. Drop the function
so people have to use git_patch_to_buf instead - git_buf has a dedicated
destructor.
Returning library-allocated strings from libgit2 works fine on Linux,
but may cause problems on Windows because there is no one C Runtime that
everything links against. With libgit2 not exposing its own allocator,
freeing the string is a gamble.
git_patch_to_str already serializes to a buffer, then returns the
underlying memory. Expose the functionality directly, so callers can use
the git_buf_free function to free the memory later.
Instead of having functions with so very many parameters to pass
hunk and line data, this takes the existing git_diff_hunk struct
and extends it with more hunk data, plus adds a git_diff_line.
Those structs are used to pass back hunk and line data instead of
the old APIs that took tons of parameters.
Some work that was previously only being done for git_diff_patch
creation (scanning the diff content for exact line counts) is now
done for all callbacks, but the performance difference should not
be noticable.
This lays groundwork for separating formatting options from diff
creation options. This groups the formatting flags separately
from the diff list creation flags and reorders the options. This
also tweaks some APIs to further separate code that uses patches
from code that just looks at git_diffs.
This makes no functional change to diff but renames a couple of
the objects and splits the new git_patch (formerly git_diff_patch)
into a new header file.
