Support RPC sequences in parser/printer
Support RPC sequences in parser/printer

We add a "sequence" data type that simply contains an ordered sequence
of productions.  We use this for RPC call and response lists.

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