Allow callers of rebase to specify custom merge options.  This may
allow custom conflict resolution, or failing fast when conflicts
are detected.

Introduce the ability to rebase in-memory or in a bare repository.

When `rebase_options.inmemory` is specified, the resultant `git_rebase`
session will not be persisted to disk.  Callers may still analyze
the rebase operations, resolve any conflicts against the in-memory
index and create the commits.  Neither `HEAD` nor the working
directory will be updated during this process.

Introduce git_commit_extract_signature

Coverity fixes

This returns the GPG signature for a commit and its contents without the
signature block, allowing for the verification of the commit's
signature.

commit: also match the first header field when searching

The function `git_packfile_stream_open` tries to free the passed
in stream when an error occurs. The only call site is
`git_indexer_append`, though, which passes in the address of a
stream struct which has not been allocated on the heap.

Fix the issue by simply removing the call to free. In case of an
error we did not allocate any memory yet and otherwise it should
be the caller's responsibility to manage it's object's lifetime.

We were searching only past the first header field, which meant we were
unable to find e.g. `tree` which is the first field.

While here, make sure to set an error message in case we cannot find the
field.

Coverity fixes

Better document `git_merge_commits` redux

`git_merge_commits` and `git_merge` now *do* handle recursive base
building for criss-cross merges.  Remove the documentation that says
that they do not.

This reverts commit 5e44d9bc.

mailmap: add ethomson@github.com

When copying contents of the cURL certiinfo we duplicate the
data but forget to actually put it into the vector.

Introduce Contributor Covenant

Free allocated pointer to curl stream on error

winhttp: name mangle class / iid on mingw

Export git_stash_apply_init_options

Fix typo

Fix a typo in documentation

Standard Windows type systems define CLSID_InternetSecurityManager
and IID_IInternetSecurityManager, but MinGW lacks these definitions.
As a result, we must hardcode these definitions ourselves.  However,
we should not use a public struct with those names, lest another
library do the same thing and consumers cannot link to both.

Make packfile_unpack_compressed a private API

Fix some issues with generated pkg-config file

ssh_stream_read(): fix possible *bytes_read < 0 branch

index: get rid of the locking

We don't support using an index object from multiple threads at the same
time, so the locking doesn't have any effect when following the
rules. If not following the rules, things are going to break down
anyway.

Handle dotfiles as the repo template dir and inside the template dir