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()
Added GetParentList(start,end) function to generate all supertype paths.
BallparkCountTests has better name, moved to top, moved guestimates to variables.
SupertypePathsTestCase, 2 simple checks - counting paths found.
Testing that supertype paths are not found in their inverse direction.
Simplified GetParentList to assume paths are to Thing, unless told otherwise.