Going forward, we will have to change how blob sizes are calculated
based on whether the blob is a cahed object part of the ODB or not. In
order to not have to distinguish between those two object types
repeatedly when accessing the blob's data or size, encapsulate all
existing direct uses of those fields by instead using
`git_blob_rawcontent` and `git_blob_rawsize`.

The `git_walk_objects` structure is currently only being used inside of
the pack-objects.c file, but being declared in its header. This has
actually been the case since its inception in 04a36fef (pack-objects:
fill a packbuilder from a walk, 2014-10-11) and has never really
changed.

Move the struct declaration into pack-objects.c to improve code
encapsulation.

Fix last references to deprecated git_buf_free

revwalk: avoid walking the entire history when output is unsorted

Signed-off-by: Sven Strickroth <email@cs-ware.de>

Add mailmap support.

tree: remove unused functions

Link `mbedTLS` libraries in when `SHA1_BACKEND` == "mbedTLS"

editorconfig: allow trailing whitespace in markdown

Also matches git.

This matches git.

Not that it matters much anyway but...

docs: fix statement about tab width

diff: fix enum value being out of allowed range

The libgit2 project mostly follows the coding style of git and thus
the linux project. While those two projects use a recommended tab width
of eight spaces, we instruct users to set their editor's tab width to
four spaces. Fix this to say eight instead.