add metadata support

NOTE: will ammend when done.

some files store lap/session summary- and metadata separately.

Added core support to Store and Marker to process this metadata.

Filter::Info now supports to add missing data to a metadata hash.
This allows the metadata to override calculated data.

Converted existing metadata to use new "meta hash":
 sport
 note
 manufacturer -> manufacturer (as string)
 device
 product -> device (as string)
 serial
 soft_version
 hard_version
 expenditure (kcal) -> work_expended (Joule)
 athletename
 athlete -> hr_rest, hr_capacity, vo2max, weight
 circum
 zeropos
 slope
 sumdur -> dur
 sumdurstop -> dur_gap

Further summary/metadata will be added in further commits