Documentation of RRi doesn't mention left/right/midpoint

[mahrud]

For some reason the documentation for RRi does not mention or even list left and right in the "Methods that use a real interval" section. Same with midpoint.

In fact, methods RRi doesn't list them and methods midpoint is empty, all probably because they are compiled functions and they're not listed in typicalvalues. I wish this could trigger an error to force us to explicitly declare the methods, or at least enumerate the missing methods.

[mahrud]

I assigned this to you, if you don't mind, since you wrote all of the documentation for intervals.

Also, it would be nice to move doc15.m2 into something more descriptive, like doc_intervals.m2 or just intervals.m2