Add next and prev attributes

[matyaskopp]

There are multiple types of document order, TEI documents can be linked with @next and @prev attributes (doc)

full order

Place all TEI files on one timeline. Probably the best place for @next and @prev is the root /TEI

partial order

Add @next and @prev to the //meeting with equal @ana (term, meeting, sitting, agenda) and @n:

        <meeting ana="#parla.term #parla.lower #parliament.PSP8" n="ps2017">ps2017</meeting>
        <meeting ana="#parla.meeting #parla.lower" n="ps2017/030">ps2017/030</meeting>
        <meeting ana="#parla.sitting #parla.lower" n="ps2017/030/07">ps2017/030/07</meeting>
        <meeting ana="#parla.agenda #parla.lower" n="ps2017/030/016">ps2017/030/016</meeting>

need to be thought out

1. Managing continual corpus increase.