add support for subsections

SHOW ENGINE INNODB STATUS in percona 5.5 may include subsections such as below which breaks the current parser.  Only tested against the data below, so may have unintended consequences.

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ROW OPERATIONS
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0 queries inside InnoDB, 0 queries in queue
1 read views open inside InnoDB
---OLDEST VIEW---
Normal read view
Read view low limit trx n:o 99B6EF2
Read view up limit trx id 99B6EF2
Read view low limit trx id 99B6EF2
Read view individually stored trx ids:
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Main thread process no. 3328, id 140214808643328, state: flushing log
Number of rows inserted 145554, updated 735808, deleted 25854, read 7725121678
0.00 inserts/s, 0.00 updates/s, 0.00 deletes/s, 0.00 reads/s
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