feat: support tcsh

[sigoden]

Usage:

./script/setup-shell.sh tcsh

Add the following code to '~/.tcshrc'

# argc-completions
setenv ARGC_COMPLETIONS_ROOT  "/tmp/argc-completions"
setenv ARGC_COMPLETIONS_PATH "$ARGC_COMPLETIONS_ROOT/completions"
setenv PATH "$ARGC_COMPLETIONS_ROOT/bin\:$PATH"
set autolist
set ARGC_TCSH_SCRIPTS=`ls -p -1 "$ARGC_COMPLETIONS_ROOT/completions" | sed -n 's/\.sh$//p'`
eval `argc --argc-completions tcsh $ARGC_TCSH_SCRIPTS`

Note: even though sigoden/argc#276 has been merged, support for tcsh will only be available after the new version of argc is released.