Added `stringer` annotations to `git.go` for `ErrorClass` and
`ErrorCode`. Added `generate` rule for `Makefile` to generate
string representations for these types (first building cgo files
in `_obj` dir to get C constants). Finally, updated `ci` actions
workflow to check that generated files are up to date.
Fixes: #543
This change:
* Updates the GitHub actions so that they run different commands for the
dynamic and static flavors of libgit2.
* Updates the .travis.yml file so that it does roughly the same as the
GitHub actions.
* Adds the release-* branches to the CI configurations.
CGO can perform variable substitution in the directives, so we don't
need to use a script to set up the variables; we can let the go tool do
it for us.
The cgo directives let us do a lot more than I previously thought, so we
can use this to make the building process of git2go go through the go
tool directly rather than via the script.
libgit2 still needs to be built manually, so we do still require make,
but only for building libgit2. Once that's built, any modifications to
git2go's own code can be built with
go build