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

When creating and printing diffs, deal with binary deltas that have
binary data specially, versus diffs that have a binary file but lack the
actual binary data.

Instead of skipping printing a binary diff when there is no data, skip
printing when we have a status of `UNMODIFIED`.  This is more in-line
with our internal data model and allows us to expand the notion of
binary data.

In the future, there may have no data because the files were unmodified
(there was no data to produce) or it may have no data because there was
no data given to us in a patch.  We want to treat these cases
separately.

When showing copy information because we are duplicating contents,
for example, when performing a `diff --find-copies-harder -M100 -B100`,
then show copy from/to lines in a patch, and do not show context.
Ensure that we can also parse such patches.

Like `git_patch_to_buf`, provide a simple helper method that can
print an entire diff directory to a `git_buf`.

`oid_strlen` has meant one more than the length of the string.
This is mighty confusing.  Make it mean only the string length!
Whomsoever needs to allocate a buffer to hold a string can null
terminate it like normal.