Add special value for scalar shape, change default shape meaning

[rly]

Fix #36

[oruebel]

Please also update here: https://github.com/NeurodataWithoutBorders/nwb-schema-language We should probably make that repo a fork, or make the data_type name key somehow configurable in the docs since that is really the only main difference.

[rly]

Please also update here: NeurodataWithoutBorders/nwb-schema-language We should probably make that repo a fork, or make the data_type name key somehow configurable in the docs since that is really the only main difference.

Will do. It is already a fork so we can update it easily.