For similarity corpora from in 0.2

Right now if we merge #8

We will lose:
- [ ] SWSC
- [ ] WordSim353

Old code is at:

- https://github.com/JuliaText/CorpusLoaders.jl/blob/65f349bbdf285fc3dda4139454e0b59079174ab9/src/similarity.jl

It needs porting to the new style
These are not traditional shaped corpora being for tasks.
Will need to think on best representation

Start by reviewing the old implementation in src/similarity.jl at the referenced commit and inspect how merging #8 affects these loaders. Decide how SWSC and WordSim353 should be represented in the new style, then port both corpora and verify they remain available after the change.

Written by the indexing model from the issue text.