pat: Add full suite of numeric expressions

[timbray]

Issue #27 is just arranging that pattern

{"x": [ 35 ]}

Will match both of the following:

{"x": 35.0}
{"x": 3.5e1}

This new issue calls for the full suite of arithmetic expressions supported by event-ruler, for example:

{"x": [ { "numeric": [ ">", 0, "<=", 5 ] } ] }

[sathishdv]

@timbray Any plans of including numeric expressions sooner?

[timbray]

I've been focused for a few weeks on implementing regular expressions, which turns out to be quite difficult. I predict that it's another month before I'm happy with the progress and ready to turn to something else.

Note that there is a full implementation of numeric expressions in aws/event-ruler and I think its design is basically OK, so if someone else wanted to pick up this work it would be a porting task not requiring algorithm invention, and (very important) there is a full set of unit tests for free that you just have to translate from Java to Go.

Having said all that, when I stop working on regular expressions I guess numeric expressions would be the next target.