The xml annotations currently used allow for marshalling of
the test suites but fail to unmarshal them because of the
lack of an xml annotation on the slice fields for test suites
and test cases.
By adding those annotations, these types can be more widely reused.
Fixes#92
Mainly:
* Moving the averaging/merging of benchmarks from the parser to the formatter package
* Tightening up the regex so it only captures the numeric values (no more of trimming spaces and the ns/op)
* Deleting the writing up in xml file the benchmark memory sections of B/op and Allocs/op
Also added a test case for parseNanoseconds().
