Shell completion fails for commands with dash in their name

[stellingsimon]

Thank you for this beautiful library. I'm enjoying it very much!

I found the following bug related to Bash completion:

When a command contains a dash in its name, e.g.

class Entity : CliktCommand(name = "crud-entity")

its arguments/options cannot be completed successfully, instead an error message appears on the prompt:

$ mytool crud-entity <TAB>
_mytool_crud-entity: command not found

The reason is the following: the generated Bash script contains an error:

    case "${COMP_WORDS[$i]}" in
      crud-entity)
        _mytool_crud-entity $(( i + 1 )) # note the dash. Bash does not allow dashes as part of a function name, so this cannot work!
        return
        ;;

# ...

_mytool_crud_entity() { # note the underscore. The function is defined correctly.
  local i=$1
  local in_param=''
# ...