Merge pull request libgit2#3739 from ethomson/0.24.1

Backport bug fixes to 0.24

Merge pull request libgit2#3653 from libgit2/cmn/treebuilder-submodule

treebuilder: don't try to verify submodules exist in the odb

openssl: re-export the last-resort locking function

We need to include the header where we define the function. Otherwise it
won't be available on the DLL.

Bump version to 0.23.4

Merge pull request libgit2#3452 from ethomson/0.23_xdiff

0.23 xdiff

Bump version to 0.23.2

Bump version to v0.23.1

Update CHANGELOG with the release number

Merge pull request libgit2#3290 from libgit2/cmn/filter-doc

filter: add docs for streaming filters

CHANGELOG: add submodule changes