Add examples

Signed-off-by: Oleg Bulatov <dmage@yandex-team.ru>
Add hack for 'cat <<\EOF'

Signed-off-by: Oleg Bulatov <dmage@yandex-team.ru>
Accept 'echo 2>&1</dev/null'

Signed-off-by: Oleg Bulatov <dmage@yandex-team.ru>
Support _ in variables names

Signed-off-by: Oleg Bulatov <dmage@yandex-team.ru>