Datadotworld

Convert README from Markdown to reStructuredText

- Add warning for outdated local datasets
- Fix config migration in case of malformed ~/.data.world
- Relax validation of file names in dataset API responses to allow slashes
- Improve content in help(datadotworld)
- Return newly created dataset URL
- Version and README updates in preparation for PyPI release

- Pull query results in application/sparql-results+json format
- Map metadata to Table Schema
- Apply schema to query results (table and dataframe)
- Expose query result schema
- Extra: Keep legacy ~/.data.world post-migration in case it's used by R SDK
- Extra: fix 18

- Map date fields to datetime dtype (pandas.DataFrame)
- Convert defunct gyear and gyearmonth types to current year and yearmonth
- Degrade gracefully in case of lack of support for year, yearmonth and duration types
- Improve messaging around schema errors

- Add wrapper methods for REST API (try: `datadotworld.api_client()`)
- Introduce support for datapackages (try: `datadotworld.load_dataset()`)
- Refactor query functions (try: `datadotworld.query()`)
- Consolidate package interface (simply `import datadotworld`, no need to instantiate `DataDotWorld`)
- Introduce unit tests
- Introduce configuration tool (try: `$ dw configure`)