feat: support flag command

[sigoden]

Flag command has command name startsWith -.
Use pacman as example:

# @cmd
# @alias -Q
# @option -i  --info           view package information (-ii for backup files)
--query() {
  :;
}

# @cmd
# @alias -S
# @option  -s  --search <regex> search remote repositories for matching strings
--sync() {
  :;
}

$ pacman -Qi vim

$ pacman -Ss '^vim-'