initial python3 support
Clear model button; bug fixes:

- build docs on Windows
- toggle primary/secondary working again
- more unicode fixes
Conserve map id, name, description. Validate map features that are not in jsonschema.

- bug fix for Builder options
- new tests for escher.validate and escher.convert_map
Merge pull request #73 from zakandrewking/python3

initial python3 support