Gita

new features
- add `commit_time` information item
- support local configuration: the intended use is a repo that contains other repos.
- Local configuration files are saved at such repos (called main repos) and they shadow the global configuration if `gita` is run inside main repos
- Sub-repos are added recursively in the local config
- Main repos are added to global config
- Main repos are displayed with underline in `gita ll`

refactoring
- Change repo configuration file from `~/.config/gita/repo_path` to `~/.config/gita/repos.csv`. To upgrade, user needs to rename the existing file accordingly.

bug fixes
- load yaml file in safe mode
- update group config file when its member repo is renamed
- fix traceback in `freeze` when the repo has no remote URL

- change `gita ll -n` to `gita ll -C` for disable coloring
- add `gita color set <situation> <color>` command to change the coloring scheme of local/remote relationship
- add `gita freeze` to show URL, name, and path of all repos
- add `gita clone <config-file>` to clone repos to cwd
- add `gita shell` command to run shell commands
- display help message for most commands (use `description` instead of `help` for subparser)
- add `gita group rmrepo` command to remove repo(s) from a group
- display tag name instead of `HEAD` when a tag is checked out
- fix traceback when deleting current context

- add `-r` option for recursive adding repos in given paths
- remove `ungroup` sub-command, and clean up `group` sub-command by adding `ll`, `add`, `rm` sub-sub-commands
- add `context` sub-command
- add `--name` to the `gita group add` command and no longer ask for user input
- add `gita group ls` command
- add `gita group rename` command
- add `--no-colors` for `gita ll` command
- add `gita color` sub-command to display current color scheme
- disallow user-defined information item

- add auto-completion script for zsh
- increase test coverage
- remove comma in the gita group display

- change the `groups.yml` config file format from `group1: repo1 repo2` to `group1: [repo1, repo2]`
- add test coverage

Note this release breaks the group format saved in `~/.config/gita/groups.yml`.

- allow customization of the `gita ll` content
- print repo name before the output of the delegated git commands
- fix README.md encoding
- add `gita group` and `gita ungroup` commands
- allow all delegated git command to take group names as input