Add more testing, docs, and fix bug
Add more testing, docs, and fix bug

- Add more testing in selftest (cover all expected use cases)
- Add documentation at the top explaining what one should expect
- Fix a bug where a statement without an argument would raise an error

heryii/snabb,snabbco/snabb,snabbco/snabb,SnabbCo/snabbswitch,Igalia/snabb,Igalia/snabbswitch,Igalia/snabbswitch,Igalia/snabb,eugeneia/snabbswitch,eugeneia/snabbswitch,eugeneia/snabb,alexandergall/snabbswitch,dpino/snabb,heryii/snabb,dpino/snabbswitch,snabbco/snabb,eugeneia/snabb,heryii/snabb,eugeneia/snabbswitch,heryii/snabb,eugeneia/snabb,dpino/snabbswitch,eugeneia/snabb,heryii/snabb,dpino/snabb,alexandergall/snabbswitch,alexandergall/snabbswitch,snabbco/snabb,alexandergall/snabbswitch,dpino/snabb,Igalia/snabb,dpino/snabb,snabbco/snabb,eugeneia/snabb,Igalia/snabb,Igalia/snabb,alexandergall/snabbswitch,Igalia/snabbswitch,dpino/snabb,alexandergall/snabbswitch,SnabbCo/snabbswitch,eugeneia/snabb,alexandergall/snabbswitch,dpino/snabb,dpino/snabbswitch,dpino/snabb,dpino/snabbswitch,Igalia/snabb,Igalia/snabb,snabbco/snabb,eugeneia/snabb,Igalia/snabbswitch,eugeneia/snabbswitch,eugeneia/snabb,snabbco/snabb,Igalia/snabbswitch,Igalia/snabb,SnabbCo/snabbswitch,SnabbCo/snabbswitch,heryii/snabb,alexandergall/snabbswitch,snabbco/snabb