Adds reader for multiline formeta records

The `FormetaDecoder` processes only individual records. If the
`LineReader` or `RecordReader` modules are used for splitting an input
stream consisting of a sequence of formeta records, this is quite
inconvenient as records either have to by in a single line or must be
seperated with a record separater character. As such a character is not
defined for the formeta format this is not a good solution.

However, the structure of formeta allows to recognise the end of a
record quite easily without having to properly parse the record. The new
module `FormetaRecordsReader` implements such a splitter. It splits a
sequence of formeta records between each record.
Fixed typo in one of the metastream readers

The reader was called formata but it should be formeta.
Added multiline support to `FormetaReader`.

Changed the `FormetaReader` to use `FormetaRecordsReader` for
record plitting instead of the `LineReader` module. This allows to
process sequences of multi-line formeta records.
Allow different result types in test cases.

Up to now the result section of a metamorph test case had to be
specified in cg-xml. This is now changed and any format which is
supported by a `Reader` can be used.