New selection operators

[lilyminium]

trafficstars

• Added 'to' operator, negatives, scientific notation, and arbitrary whitespace for ranges (Issue #3054, PR #2927)
• Added atol and rtol keywords for float comparison (PR #2927)

The selections page should get updated to explain and demonstrate these.

Possibly we can upload one of the basic workshop notebooks into binder as a playground for people to try it out.