Add RDFS for type and attribute pages

Includes properties such as:
* rdfs:comment
* rdfs:label
* rdfs:subClassOf

With this patch, individual type and attribute pages will now express basic
RDFS; classes will express their immediate subclass relationship and all
of the properties that can be applied to them, while attributes express
their domainIncludes values.

Addresses #24

Signed-off-by: Dan Scott <dan@coffeecode.net>
Clarify that RDFa and JSON-LD are supported formats

The getting started documentation referred to a long-term plan to
support a broader variety of formats, but RDFa and JSON-LD are
pretty tightly integrated into the rest of the schema.org documentation,
so we might as well mention them explicitly in the getting started (but
continue documenting with microdata as the default approach).

Signed-off-by: Dan Scott <dan@coffeecode.net>
Merge pull request #29 from dbs/gs_broader_serialization

Clarify that RDFa and JSON-LD are supported formats
Merge branch 'per_page_rdfs' into newmerge

Signed-off-by: Dan Scott <dan@coffeecode.net>

Conflicts:
	api.py
Merge pull request #25 from dbs/per_page_rdfs

CODE: Add RDFS for type and attribute pages
Adding isDataType() to API, with tests. As suggested by Dan Scott.

Based on https://github.com/rvguha/schemaorg/pull/30
Merge pull request #42 from danbri/master

Adding isDataType() to API, with tests. As suggested by Dan Scott.
Improve DataType handling

DataTypes such as Integer currently do not get a header generated for them, nor
do they get their subtypes enumerated, and they also get a useless property
header generated.

Use the new isDataType() method throughout the page generation to
handle DataTypes properly.

Fixes #26

Signed-off-by: Dan Scott <dan@coffeecode.net>
Merge pull request #30 from dbs/datatype_handling

CODE: Improve DataType handling
Basic JSON-LD code, with flag to enable.
Exposing json-ld at its own url in json and text mime types.
.txt vs .json.txt fix.
.*
Added a simple external mappings mechanism expressed in RDFa.

If we find an equivalentClass or equivalentProperty statement in the schema
graph, it gets reflected into the per-term documentation page.
Fixes to external mappings, including making it an option. Added some mappings.
Dropping subproperty(), use subproperties() instead. Fixed test accordingly.
Various tidying.
Dropping superproperty(), use superproperties() instead. Fixed tests accordingly.
Tidying and commenting. Removed superproperty(). Renamed getFoo() to GetFoo().
Fixed link so it doesn't hard-code http (or https), avoiding mixing the two.
GetAllTypes() relaces getAllTypes()