add a way of structuring and documenting tags

[liveandrew]

reslang currently puts each resource with its own tag, so the docs are necessarily focused on resource level descriptions

swagger allows this to be far more configurable - we should allow tags to be a first class concept in reslang

[liveandrew]

see docs here: https://github.com/LiveRamp/reslang/blob/master/docs/sections.md