Refactor parseMkv a bit
MkvParse: Expose parseMkv1 and initialParserState
Fight space leak with more bangs

(Actually I don't completely understand what happens)

There was a space leak in MkvParse that occured when I don't
use event completely (i.e. ignore EbmlElement events)
and was fixable by doing `trace (show event) $`

With this change it seems to work better