My experience is that the current `withStyles` declaration works poorly with Typescript 2.8.  
I'm not sure that it's the compiler version that's the issue, though.
At least in my usage, it fails to remove `WithStyles<ClassKey>` from the return type.

This definition works better in my experience, doesn't rely on subtle inferencer behavior in the same way, and seems to be in the mainstream of current usage.  

There's a built-in `Exclude` function in Typescript 2.8 that does what `Omit` does.
I used `Omit` for compatibility with older compilers.

Remove commented-on code from withStyles;
use ConsistentWith typewrapper;
add SFC test for withWidth
add FAILING test for doc scenario 2 (withStyles of union)

Trim obsolete doc.
Rename "decorate" function to "withMyStyles" in doc.
Remove redundant failing tests added to clarify Omit problem.

In package.json, up-rev Typescript to >2.6.2, and print Typescript
version in "typescript" run command.

Use single quotes in test.
In package.json, revert typescript to 2.6.1, remove version-printing run command
In package.lock, revert typescript to 2.6.1.

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