delete @select! reference

[pdeffebach]

In reference to #218. We shouldn't update the readme to discuss @select! and @transform! until we make a new release.

I would rather wait for a new release until we have @subset and @subset! and maybe and @orderby!.

cc @nalimilan

[bkamins]

Though I would remove the documentation from README.md entirely

[pdeffebach]

I think the best solution is to take the current version of the readme and make it the docstring for the module. Then we can add to that as needed. Then before releases we just copy over the docstring as is to the actual readme.

[nalimilan]

There's already a list of provided function in the homepage of the Documenter manual. So why not remove the list from the README completely? I don't think it's standard to have a docstring for a module listing all functions it exports: Documenter does that automatically already so adding a manual list which is likely to get outdated isn't great.

[pdeffebach]

Okay, updated to delete the list of macros entirely. With an approval I will merge.