Constructor of interval that contains number not represented exactly by IEEE 754

[markcampanelli]

Thanks for making this interval package available publicly. I have found it useful for making "gold" datasets for verifying and benchmarking competing numerical algorithms to solve the same problem.

I would like to pyinterval to have a constructor that will return the smallest interval (with exact IEEE 754 endpoints) that contains a number passed in as an "exact" decimal representation as a string.

For example,

x = interval('0.1')

would return the smallest interval (with exact IEEE 754 endpoints) containing 0.1.

Also, it would be very helpful to be able to turn on a "full precision" mode that shows all interval endpoints at full (decimal) precision. A hexidecimal option here would make things more compact as well (cf. https://docs.python.org/3/library/functions.html#hex).