new-feature: local mode; support using git-remote
- changes of CLI:
- `--asset-dir` is removed.
- `--output-dir`: the root git dir to push to remote, which contains
converted assets. A git repo will be initialized in this dir.
- `--asset-output-dir`: the dir to store assets. Most cases you do
not need to set this path.
- changes of github-action:
- `md_branch` is removed. Now it always pushes to the branch it
converts md from.
- new-feature: support specifying a remote as url of the repo that
stores converted assets.
- new-feature: if `--repo` is not specified, it convert md locally,
i.e., assets are linked by relative path, and nothing is pushed to
remote.
- test: when CI, use repo md2test to test pushing.
- refactor: extract common util func from test, such as comparing md,
comparing images.
- refactor: use feature-list to describe platform specific convertion.
- refactor: use k3git to parse git url.
doc: add trouble shooting
change: asset does not include platform as part of path
new-featrue: convert graphviz(dot) codes to image