new exposure schema and example
Merge branch 'master' of https://github.com/gem/oq-nrmllib into exposure-update
schema adapted to the last defined version
parser updated
allow asset without costs (for population)
remove validation on costs len (for population) in parser
removed area from the conversions returned by the parser
remove Cost prefix from the returned cost types
retrofitted cost as standard cost type
updated schema to embed retrofitted value into cost tags
fix converter
support for occupancies in converter
improved naming conventions
fixed a couple of pep8 issues
Merge pull request #94 from matley/exposure-update

Exposure schema update